Remove stale announcement from README.md (#22962)
Remove stale announcement from README.md (#22962)

We should keep these timely.
cc: da39a3ee5e6b4b0d3255bfef95601890afd80709@karelz
mmitche/corefx,nchikanov/corefx,fgreinacher/corefx,krk/corefx,axelheer/corefx,jlin177/corefx,shimingsg/corefx,BrennanConroy/corefx,twsouthwick/corefx,richlander/corefx,shimingsg/corefx,shimingsg/corefx,ericstj/corefx,rubo/corefx,JosephTremoulet/corefx,seanshpark/corefx,richlander/corefx,jlin177/corefx,parjong/corefx,krk/corefx,shimingsg/corefx,ptoonen/corefx,ericstj/corefx,shimingsg/corefx,mmitche/corefx,Jiayili1/corefx,the-dwyer/corefx,Jiayili1/corefx,seanshpark/corefx,JosephTremoulet/corefx,the-dwyer/corefx,MaggieTsang/corefx,zhenlan/corefx,Jiayili1/corefx,Jiayili1/corefx,ericstj/corefx,JosephTremoulet/corefx,parjong/corefx,zhenlan/corefx,seanshpark/corefx,Ermiar/corefx,ericstj/corefx,rubo/corefx,krk/corefx,the-dwyer/corefx,Ermiar/corefx,mmitche/corefx,tijoytom/corefx,seanshpark/corefx,ptoonen/corefx,wtgodbe/corefx,zhenlan/corefx,axelheer/corefx,MaggieTsang/corefx,Ermiar/corefx,ravimeda/corefx,jlin177/corefx,ptoonen/corefx,wtgodbe/corefx,seanshpark/corefx,wtgodbe/corefx,ViktorHofer/corefx,ptoonen/corefx,tijoytom/corefx,wtgodbe/corefx,nchikanov/corefx,fgreinacher/corefx,the-dwyer/corefx,axelheer/corefx,Ermiar/corefx,ravimeda/corefx,ViktorHofer/corefx,nchikanov/corefx,ericstj/corefx,MaggieTsang/corefx,krk/corefx,ravimeda/corefx,tijoytom/corefx,ravimeda/corefx,twsouthwick/corefx,wtgodbe/corefx,ViktorHofer/corefx,mmitche/corefx,jlin177/corefx,mmitche/corefx,axelheer/corefx,BrennanConroy/corefx,Jiayili1/corefx,twsouthwick/corefx,MaggieTsang/corefx,zhenlan/corefx,the-dwyer/corefx,ViktorHofer/corefx,mmitche/corefx,fgreinacher/corefx,zhenlan/corefx,twsouthwick/corefx,mazong1123/corefx,mazong1123/corefx,ravimeda/corefx,zhenlan/corefx,tijoytom/corefx,Jiayili1/corefx,ravimeda/corefx,rubo/corefx,JosephTremoulet/corefx,seanshpark/corefx,mmitche/corefx,richlander/corefx,richlander/corefx,mazong1123/corefx,Ermiar/corefx,Ermiar/corefx,parjong/corefx,the-dwyer/corefx,JosephTremoulet/corefx,tijoytom/corefx,jlin177/corefx,axelheer/corefx,richlander/corefx,tijoytom/corefx,mazong1123/corefx,parjong/corefx,Ermiar/corefx,ViktorHofer/corefx,richlander/corefx,tijoytom/corefx,nchikanov/corefx,parjong/corefx,parjong/corefx,nchikanov/corefx,nchikanov/corefx,twsouthwick/corefx,ptoonen/corefx,BrennanConroy/corefx,rubo/corefx,MaggieTsang/corefx,parjong/corefx,krk/corefx,seanshpark/corefx,twsouthwick/corefx,ericstj/corefx,ravimeda/corefx,axelheer/corefx,shimingsg/corefx,mazong1123/corefx,richlander/corefx,ViktorHofer/corefx,JosephTremoulet/corefx,krk/corefx,jlin177/corefx,krk/corefx,twsouthwick/corefx,MaggieTsang/corefx,Jiayili1/corefx,fgreinacher/corefx,mazong1123/corefx,shimingsg/corefx,wtgodbe/corefx,rubo/corefx,the-dwyer/corefx,ViktorHofer/corefx,jlin177/corefx,ptoonen/corefx,wtgodbe/corefx,ericstj/corefx,ptoonen/corefx,MaggieTsang/corefx,zhenlan/corefx,nchikanov/corefx,JosephTremoulet/corefx,mazong1123/corefx