Fix Obsolete build warnings in System.Security.Cryptography.Encoding
Fix Obsolete build warnings in System.Security.Cryptography.Encoding

The build had these three warnings:
```
\corefx\src\Common\src\Interop\Windows\Crypt32\OidInfo.cs(83,48): warning CS0618: 'Marshal.PtrToStructure(IntPtr, Type)' is obsolete
: 'PtrToStructure(IntPtr, Type) may be unavailable in future releases. Instead, use PtrToStructure<T>(IntPtr). For more info, go to http://go.microsoft.com/fwl
ink/?LinkID=296513' [\corefx\src\System.Security.Cryptography.Encoding\src\System.Security.Cryptography.Encoding.csproj]
\corefx\src\Common\src\Interop\Windows\Crypt32\OidInfo.cs(91,44): warning CS0618: 'Marshal.PtrToStructure(IntPtr, Type)' is obsolete
: 'PtrToStructure(IntPtr, Type) may be unavailable in future releases. Instead, use PtrToStructure<T>(IntPtr). For more info, go to http://go.microsoft.com/fwl
ink/?LinkID=296513' [\corefx\src\System.Security.Cryptography.Encoding\src\System.Security.Cryptography.Encoding.csproj]
\corefx\src\Common\src\Interop\Windows\Crypt32\OidInfo.cs(101,48): warning CS0618: 'Marshal.PtrToStructure(IntPtr, Type)' is obsolet
e: 'PtrToStructure(IntPtr, Type) may be unavailable in future releases. Instead, use PtrToStructure<T>(IntPtr). For more info, go to http://go.microsoft.com/fw
link/?LinkID=296513' [\corefx\src\System.Security.Cryptography.Encoding\src\System.Security.Cryptography.Encoding.csproj]
```

shiftkey-tester/corefx,shahid-pk/corefx,the-dwyer/corefx,wtgodbe/corefx,wtgodbe/corefx,bitcrazed/corefx,huanjie/corefx,akivafr123/corefx,gkhanna79/corefx,richlander/corefx,yizhang82/corefx,mmitche/corefx,janhenke/corefx,alphonsekurian/corefx,gkhanna79/corefx,marksmeltzer/corefx,mokchhya/corefx,axelheer/corefx,690486439/corefx,YoupHulsebos/corefx,dotnet-bot/corefx,ellismg/corefx,stephenmichaelf/corefx,shimingsg/corefx,gregg-miskelly/corefx,cartermp/corefx,vs-team/corefx,jhendrixMSFT/corefx,andyhebear/corefx,kyulee1/corefx,zhangwenquan/corefx,twsouthwick/corefx,MaggieTsang/corefx,zmaruo/corefx,parjong/corefx,gkhanna79/corefx,cydhaselton/corefx,jlin177/corefx,gkhanna79/corefx,khdang/corefx,jlin177/corefx,ericstj/corefx,SGuyGe/corefx,VPashkov/corefx,janhenke/corefx,parjong/corefx,DnlHarvey/corefx,KrisLee/corefx,josguil/corefx,nbarbettini/corefx,cydhaselton/corefx,stone-li/corefx,BrennanConroy/corefx,vrassouli/corefx,pallavit/corefx,cydhaselton/corefx,CloudLens/corefx,weltkante/corefx,krk/corefx,benjamin-bader/corefx,zhenlan/corefx,andyhebear/corefx,pgavlin/corefx,wtgodbe/corefx,krk/corefx,benjamin-bader/corefx,shimingsg/corefx,axelheer/corefx,tijoytom/corefx,nelsonsar/corefx,lggomez/corefx,rahku/corefx,s0ne0me/corefx,ViktorHofer/corefx,lggomez/corefx,comdiv/corefx,larsbj1988/corefx,zhenlan/corefx,marksmeltzer/corefx,weltkante/corefx,Petermarcu/corefx,erpframework/corefx,twsouthwick/corefx,twsouthwick/corefx,nchikanov/corefx,alexandrnikitin/corefx,josguil/corefx,cnbin/corefx,stone-li/corefx,nbarbettini/corefx,PatrickMcDonald/corefx,elijah6/corefx,mazong1123/corefx,fgreinacher/corefx,gregg-miskelly/corefx,gkhanna79/corefx,richlander/corefx,dkorolev/corefx,stephenmichaelf/corefx,benjamin-bader/corefx,JosephTremoulet/corefx,marksmeltzer/corefx,kkurni/corefx,manu-silicon/corefx,matthubin/corefx,oceanho/corefx,tijoytom/corefx,kkurni/corefx,Frank125/corefx,wtgodbe/corefx,ravimeda/corefx,gabrielPeart/corefx,mafiya69/corefx,mellinoe/corefx,shiftkey-tester/corefx,Chrisboh/corefx,josguil/corefx,thiagodin/corefx,dtrebbien/corefx,s0ne0me/corefx,yizhang82/corefx,PatrickMcDonald/corefx,benjamin-bader/corefx,tijoytom/corefx,erpframework/corefx,uhaciogullari/corefx,EverlessDrop41/corefx,alexperovich/corefx,tstringer/corefx,MaggieTsang/corefx,tijoytom/corefx,rajansingh10/corefx,cnbin/corefx,zmaruo/corefx,xuweixuwei/corefx,n1ghtmare/corefx,zhenlan/corefx,mafiya69/corefx,gregg-miskelly/corefx,Ermiar/corefx,JosephTremoulet/corefx,vijaykota/corefx,richlander/corefx,ericstj/corefx,elijah6/corefx,dkorolev/corefx,shiftkey-tester/corefx,nelsonsar/corefx,nbarbettini/corefx,krk/corefx,s0ne0me/corefx,Ermiar/corefx,Jiayili1/corefx,elijah6/corefx,Jiayili1/corefx,fffej/corefx,nchikanov/corefx,ellismg/corefx,shrutigarg/corefx,dotnet-bot/corefx,axelheer/corefx,BrennanConroy/corefx,spoiledsport/corefx,fernando-rodriguez/corefx,krk/corefx,the-dwyer/corefx,huanjie/corefx,cartermp/corefx,parjong/corefx,Chrisboh/corefx,seanshpark/corefx,comdiv/corefx,pallavit/corefx,the-dwyer/corefx,Winsto/corefx,axelheer/corefx,Priya91/corefx-1,scott156/corefx,ViktorHofer/corefx,tstringer/corefx,ericstj/corefx,seanshpark/corefx,wtgodbe/corefx,mokchhya/corefx,krytarowski/corefx,zhangwenquan/corefx,anjumrizwi/corefx,stephenmichaelf/corefx,benpye/corefx,popolan1986/corefx,shrutigarg/corefx,gabrielPeart/corefx,gregg-miskelly/corefx,ravimeda/corefx,Yanjing123/corefx,mmitche/corefx,dtrebbien/corefx,ericstj/corefx,brett25/corefx,shana/corefx,ptoonen/corefx,PatrickMcDonald/corefx,Priya91/corefx-1,zhenlan/corefx,cartermp/corefx,billwert/corefx,dotnet-bot/corefx,erpframework/corefx,YoupHulsebos/corefx,stephenmichaelf/corefx,matthubin/corefx,Petermarcu/corefx,dtrebbien/corefx,mazong1123/corefx,CherryCxldn/corefx,vrassouli/corefx,seanshpark/corefx,jlin177/corefx,mokchhya/corefx,VPashkov/corefx,tijoytom/corefx,PatrickMcDonald/corefx,cartermp/corefx,mazong1123/corefx,heXelium/corefx,comdiv/corefx,shahid-pk/corefx,MaggieTsang/corefx,thiagodin/corefx,mokchhya/corefx,dhoehna/corefx,shahid-pk/corefx,shahid-pk/corefx,claudelee/corefx,kyulee1/corefx,ViktorHofer/corefx,the-dwyer/corefx,rahku/corefx,jcme/corefx,mazong1123/corefx,rubo/corefx,rjxby/corefx,vijaykota/corefx,vidhya-bv/corefx-sorting,marksmeltzer/corefx,kkurni/corefx,kyulee1/corefx,fernando-rodriguez/corefx,EverlessDrop41/corefx,iamjasonp/corefx,scott156/corefx,YoupHulsebos/corefx,JosephTremoulet/corefx,VPashkov/corefx,misterzik/corefx,krytarowski/corefx,manu-silicon/corefx,oceanho/corefx,vs-team/corefx,jlin177/corefx,nelsonsar/corefx,SGuyGe/corefx,Petermarcu/corefx,cydhaselton/corefx,weltkante/corefx,anjumrizwi/corefx,690486439/corefx,vijaykota/corefx,alexperovich/corefx,seanshpark/corefx,stephenmichaelf/corefx,CherryCxldn/corefx,stormleoxia/corefx,destinyclown/corefx,Alcaro/corefx,ericstj/corefx,cydhaselton/corefx,thiagodin/corefx,shimingsg/corefx,chaitrakeshav/corefx,690486439/corefx,twsouthwick/corefx,twsouthwick/corefx,lggomez/corefx,rubo/corefx,s0ne0me/corefx,shmao/corefx,jhendrixMSFT/corefx,jcme/corefx,zhangwenquan/corefx,alexperovich/corefx,janhenke/corefx,the-dwyer/corefx,vidhya-bv/corefx-sorting,anjumrizwi/corefx,ellismg/corefx,DnlHarvey/corefx,mmitche/corefx,KrisLee/corefx,dhoehna/corefx,Winsto/corefx,shmao/corefx,manu-silicon/corefx,ViktorHofer/corefx,richlander/corefx,shmao/corefx,Jiayili1/corefx,SGuyGe/corefx,JosephTremoulet/corefx,bitcrazed/corefx,MaggieTsang/corefx,shahid-pk/corefx,akivafr123/corefx,nelsonsar/corefx,bpschoch/corefx,dtrebbien/corefx,pallavit/corefx,vidhya-bv/corefx-sorting,MaggieTsang/corefx,Petermarcu/corefx,tstringer/corefx,ptoonen/corefx,EverlessDrop41/corefx,brett25/corefx,fgreinacher/corefx,chenxizhang/corefx,larsbj1988/corefx,ellismg/corefx,dotnet-bot/corefx,scott156/corefx,mafiya69/corefx,kkurni/corefx,marksmeltzer/corefx,Petermarcu/corefx,tijoytom/corefx,parjong/corefx,jcme/corefx,jeremymeng/corefx,mellinoe/corefx,dhoehna/corefx,janhenke/corefx,yizhang82/corefx,heXelium/corefx,dkorolev/corefx,parjong/corefx,pallavit/corefx,kkurni/corefx,uhaciogullari/corefx,jmhardison/corefx,CherryCxldn/corefx,axelheer/corefx,alexandrnikitin/corefx,marksmeltzer/corefx,Frank125/corefx,alphonsekurian/corefx,shimingsg/corefx,nbarbettini/corefx,vs-team/corefx,jhendrixMSFT/corefx,KrisLee/corefx,comdiv/corefx,n1ghtmare/corefx,dhoehna/corefx,CloudLens/corefx,elijah6/corefx,shimingsg/corefx,benjamin-bader/corefx,nbarbettini/corefx,dsplaisted/corefx,jhendrixMSFT/corefx,YoupHulsebos/corefx,cnbin/corefx,Ermiar/corefx,chaitrakeshav/corefx,chenkennt/corefx,jcme/corefx,Chrisboh/corefx,MaggieTsang/corefx,rahku/corefx,gkhanna79/corefx,shmao/corefx,dsplaisted/corefx,lydonchandra/corefx,jlin177/corefx,chaitrakeshav/corefx,cartermp/corefx,lggomez/corefx,Alcaro/corefx,weltkante/corefx,dhoehna/corefx,seanshpark/corefx,CherryCxldn/corefx,bpschoch/corefx,dkorolev/corefx,bpschoch/corefx,pgavlin/corefx,pgavlin/corefx,seanshpark/corefx,viniciustaveira/corefx,fffej/corefx,rajansingh10/corefx,destinyclown/corefx,Priya91/corefx-1,chenxizhang/corefx,adamralph/corefx,nchikanov/corefx,dotnet-bot/corefx,iamjasonp/corefx,larsbj1988/corefx,manu-silicon/corefx,jeremymeng/corefx,DnlHarvey/corefx,bitcrazed/corefx,viniciustaveira/corefx,stormleoxia/corefx,khdang/corefx,vs-team/corefx,uhaciogullari/corefx,billwert/corefx,lggomez/corefx,billwert/corefx,viniciustaveira/corefx,josguil/corefx,parjong/corefx,vidhya-bv/corefx-sorting,nchikanov/corefx,ViktorHofer/corefx,lggomez/corefx,the-dwyer/corefx,lydonchandra/corefx,KrisLee/corefx,seanshpark/corefx,benjamin-bader/corefx,alphonsekurian/corefx,benpye/corefx,Priya91/corefx-1,n1ghtmare/corefx,andyhebear/corefx,shrutigarg/corefx,alexperovich/corefx,shana/corefx,SGuyGe/corefx,iamjasonp/corefx,larsbj1988/corefx,brett25/corefx,khdang/corefx,yizhang82/corefx,vidhya-bv/corefx-sorting,chenkennt/corefx,Chrisboh/corefx,rjxby/corefx,elijah6/corefx,mmitche/corefx,tijoytom/corefx,dsplaisted/corefx,mellinoe/corefx,josguil/corefx,Yanjing123/corefx,rjxby/corefx,bitcrazed/corefx,pallavit/corefx,DnlHarvey/corefx,Ermiar/corefx,the-dwyer/corefx,manu-silicon/corefx,matthubin/corefx,mafiya69/corefx,cartermp/corefx,billwert/corefx,rahku/corefx,cydhaselton/corefx,akivafr123/corefx,iamjasonp/corefx,dotnet-bot/corefx,shahid-pk/corefx,krytarowski/corefx,jhendrixMSFT/corefx,misterzik/corefx,heXelium/corefx,zmaruo/corefx,zhenlan/corefx,ptoonen/corefx,andyhebear/corefx,chenkennt/corefx,Ermiar/corefx,mmitche/corefx,mellinoe/corefx,shiftkey-tester/corefx,Yanjing123/corefx,benpye/corefx,CloudLens/corefx,khdang/corefx,oceanho/corefx,ViktorHofer/corefx,mafiya69/corefx,zhangwenquan/corefx,tstringer/corefx,fffej/corefx,weltkante/corefx,fffej/corefx,tstringer/corefx,richlander/corefx,nbarbettini/corefx,zhenlan/corefx,Chrisboh/corefx,xuweixuwei/corefx,stephenmichaelf/corefx,ptoonen/corefx,alexandrnikitin/corefx,DnlHarvey/corefx,nchikanov/corefx,Petermarcu/corefx,alexperovich/corefx,ravimeda/corefx,stone-li/corefx,josguil/corefx,alexandrnikitin/corefx,claudelee/corefx,jhendrixMSFT/corefx,scott156/corefx,adamralph/corefx,jmhardison/corefx,jmhardison/corefx,BrennanConroy/corefx,twsouthwick/corefx,parjong/corefx,jmhardison/corefx,wtgodbe/corefx,mafiya69/corefx,misterzik/corefx,ericstj/corefx,yizhang82/corefx,n1ghtmare/corefx,weltkante/corefx,xuweixuwei/corefx,rjxby/corefx,690486439/corefx,krk/corefx,690486439/corefx,popolan1986/corefx,SGuyGe/corefx,MaggieTsang/corefx,bitcrazed/corefx,erpframework/corefx,Alcaro/corefx,rahku/corefx,iamjasonp/corefx,kyulee1/corefx,ravimeda/corefx,CloudLens/corefx,shimingsg/corefx,rjxby/corefx,jlin177/corefx,jeremymeng/corefx,kkurni/corefx,ellismg/corefx,benpye/corefx,dhoehna/corefx,alphonsekurian/corefx,cydhaselton/corefx,iamjasonp/corefx,richlander/corefx,ellismg/corefx,alexperovich/corefx,jeremymeng/corefx,krk/corefx,rjxby/corefx,janhenke/corefx,brett25/corefx,Alcaro/corefx,shimingsg/corefx,chaitrakeshav/corefx,mazong1123/corefx,stone-li/corefx,Jiayili1/corefx,alexperovich/corefx,krk/corefx,ericstj/corefx,destinyclown/corefx,popolan1986/corefx,ravimeda/corefx,alphonsekurian/corefx,huanjie/corefx,mellinoe/corefx,Jiayili1/corefx,akivafr123/corefx,shmao/corefx,krytarowski/corefx,yizhang82/corefx,heXelium/corefx,rubo/corefx,thiagodin/corefx,lydonchandra/corefx,dotnet-bot/corefx,stormleoxia/corefx,rjxby/corefx,mellinoe/corefx,Frank125/corefx,SGuyGe/corefx,nchikanov/corefx,oceanho/corefx,elijah6/corefx,bpschoch/corefx,ptoonen/corefx,khdang/corefx,pallavit/corefx,cnbin/corefx,stone-li/corefx,vrassouli/corefx,YoupHulsebos/corefx,jhendrixMSFT/corefx,Chrisboh/corefx,jeremymeng/corefx,shrutigarg/corefx,lydonchandra/corefx,JosephTremoulet/corefx,Ermiar/corefx,rahku/corefx,shmao/corefx,mmitche/corefx,Petermarcu/corefx,anjumrizwi/corefx,Yanjing123/corefx,YoupHulsebos/corefx,rajansingh10/corefx,Jiayili1/corefx,DnlHarvey/corefx,PatrickMcDonald/corefx,Frank125/corefx,krytarowski/corefx,shana/corefx,gabrielPeart/corefx,gabrielPeart/corefx,axelheer/corefx,rubo/corefx,mazong1123/corefx,rubo/corefx,elijah6/corefx,jcme/corefx,fgreinacher/corefx,uhaciogullari/corefx,adamralph/corefx,ravimeda/corefx,JosephTremoulet/corefx,janhenke/corefx,benpye/corefx,jcme/corefx,chenxizhang/corefx,stone-li/corefx,alphonsekurian/corefx,rajansingh10/corefx,nchikanov/corefx,alphonsekurian/corefx,mmitche/corefx,benpye/corefx,Ermiar/corefx,spoiledsport/corefx,manu-silicon/corefx,akivafr123/corefx,matthubin/corefx,vrassouli/corefx,Priya91/corefx-1,khdang/corefx,mazong1123/corefx,stone-li/corefx,richlander/corefx,huanjie/corefx,shmao/corefx,viniciustaveira/corefx,marksmeltzer/corefx,Priya91/corefx-1,zmaruo/corefx,ptoonen/corefx,mokchhya/corefx,ViktorHofer/corefx,manu-silicon/corefx,weltkante/corefx,rahku/corefx,wtgodbe/corefx,fernando-rodriguez/corefx,claudelee/corefx,YoupHulsebos/corefx,billwert/corefx,yizhang82/corefx,Winsto/corefx,nbarbettini/corefx,stephenmichaelf/corefx,VPashkov/corefx,pgavlin/corefx,stormleoxia/corefx,DnlHarvey/corefx,jlin177/corefx,fgreinacher/corefx,shana/corefx,dhoehna/corefx,spoiledsport/corefx,JosephTremoulet/corefx,ravimeda/corefx,twsouthwick/corefx,krytarowski/corefx,billwert/corefx,ptoonen/corefx,mokchhya/corefx,gkhanna79/corefx,billwert/corefx,zhenlan/corefx,iamjasonp/corefx,alexandrnikitin/corefx,claudelee/corefx,Jiayili1/corefx,krytarowski/corefx,tstringer/corefx,lggomez/corefx,Yanjing123/corefx,n1ghtmare/corefx