Remove unneeded field from BinaryWriter (#8015)
Remove unneeded field from BinaryWriter (#8015)

The field only exists in .NET Framework for serialization compat. It
isn't needed on CoreCLR.
tijoytom/coreclr,cshung/coreclr,yeaicc/coreclr,russellhadley/coreclr,James-Ko/coreclr,sagood/coreclr,wtgodbe/coreclr,YongseopKim/coreclr,cmckinsey/coreclr,James-Ko/coreclr,cshung/coreclr,botaberg/coreclr,krk/coreclr,ragmani/coreclr,mmitche/coreclr,neurospeech/coreclr,ruben-ayrapetyan/coreclr,parjong/coreclr,alexperovich/coreclr,tijoytom/coreclr,JonHanna/coreclr,rartemev/coreclr,qiudesong/coreclr,parjong/coreclr,pgavlin/coreclr,rartemev/coreclr,neurospeech/coreclr,JonHanna/coreclr,mskvortsov/coreclr,cmckinsey/coreclr,kyulee1/coreclr,sjsinju/coreclr,mskvortsov/coreclr,krytarowski/coreclr,pgavlin/coreclr,yizhang82/coreclr,qiudesong/coreclr,pgavlin/coreclr,YongseopKim/coreclr,gkhanna79/coreclr,gkhanna79/coreclr,ruben-ayrapetyan/coreclr,cmckinsey/coreclr,kyulee1/coreclr,krytarowski/coreclr,mmitche/coreclr,wtgodbe/coreclr,JosephTremoulet/coreclr,qiudesong/coreclr,gkhanna79/coreclr,neurospeech/coreclr,JosephTremoulet/coreclr,cydhaselton/coreclr,hseok-oh/coreclr,botaberg/coreclr,sagood/coreclr,kyulee1/coreclr,wateret/coreclr,ragmani/coreclr,wateret/coreclr,dpodder/coreclr,cshung/coreclr,krytarowski/coreclr,alexperovich/coreclr,mmitche/coreclr,JonHanna/coreclr,tijoytom/coreclr,russellhadley/coreclr,alexperovich/coreclr,wateret/coreclr,poizan42/coreclr,James-Ko/coreclr,krytarowski/coreclr,cshung/coreclr,krk/coreclr,cmckinsey/coreclr,yeaicc/coreclr,cshung/coreclr,botaberg/coreclr,rartemev/coreclr,ruben-ayrapetyan/coreclr,YongseopKim/coreclr,jamesqo/coreclr,sagood/coreclr,hseok-oh/coreclr,neurospeech/coreclr,cmckinsey/coreclr,kyulee1/coreclr,yeaicc/coreclr,mmitche/coreclr,cshung/coreclr,rartemev/coreclr,yizhang82/coreclr,cydhaselton/coreclr,jamesqo/coreclr,sjsinju/coreclr,ragmani/coreclr,tijoytom/coreclr,jamesqo/coreclr,russellhadley/coreclr,cmckinsey/coreclr,gkhanna79/coreclr,russellhadley/coreclr,ruben-ayrapetyan/coreclr,pgavlin/coreclr,yeaicc/coreclr,ragmani/coreclr,alexperovich/coreclr,krytarowski/coreclr,sagood/coreclr,JosephTremoulet/coreclr,JonHanna/coreclr,poizan42/coreclr,hseok-oh/coreclr,krk/coreclr,yizhang82/coreclr,wtgodbe/coreclr,botaberg/coreclr,alexperovich/coreclr,botaberg/coreclr,poizan42/coreclr,kyulee1/coreclr,YongseopKim/coreclr,cydhaselton/coreclr,dpodder/coreclr,qiudesong/coreclr,YongseopKim/coreclr,krk/coreclr,sagood/coreclr,dpodder/coreclr,ruben-ayrapetyan/coreclr,wateret/coreclr,jamesqo/coreclr,hseok-oh/coreclr,JonHanna/coreclr,wateret/coreclr,JonHanna/coreclr,ragmani/coreclr,James-Ko/coreclr,JosephTremoulet/coreclr,sjsinju/coreclr,gkhanna79/coreclr,dpodder/coreclr,sjsinju/coreclr,russellhadley/coreclr,russellhadley/coreclr,mskvortsov/coreclr,AlexGhiondea/coreclr,cydhaselton/coreclr,wateret/coreclr,AlexGhiondea/coreclr,yizhang82/coreclr,sjsinju/coreclr,dpodder/coreclr,cydhaselton/coreclr,James-Ko/coreclr,wtgodbe/coreclr,wtgodbe/coreclr,AlexGhiondea/coreclr,cydhaselton/coreclr,sagood/coreclr,yeaicc/coreclr,ragmani/coreclr,qiudesong/coreclr,botaberg/coreclr,parjong/coreclr,krk/coreclr,jamesqo/coreclr,parjong/coreclr,yeaicc/coreclr,poizan42/coreclr,cmckinsey/coreclr,parjong/coreclr,jamesqo/coreclr,AlexGhiondea/coreclr,ruben-ayrapetyan/coreclr,dpodder/coreclr,yizhang82/coreclr,krk/coreclr,JosephTremoulet/coreclr,James-Ko/coreclr,AlexGhiondea/coreclr,poizan42/coreclr,tijoytom/coreclr,parjong/coreclr,tijoytom/coreclr,hseok-oh/coreclr,mmitche/coreclr,mmitche/coreclr,YongseopKim/coreclr,hseok-oh/coreclr,neurospeech/coreclr,alexperovich/coreclr,sjsinju/coreclr,mskvortsov/coreclr,yeaicc/coreclr,mskvortsov/coreclr,neurospeech/coreclr,krytarowski/coreclr,pgavlin/coreclr,mskvortsov/coreclr,yizhang82/coreclr,rartemev/coreclr,JosephTremoulet/coreclr,pgavlin/coreclr,qiudesong/coreclr,rartemev/coreclr,gkhanna79/coreclr,kyulee1/coreclr,AlexGhiondea/coreclr,wtgodbe/coreclr,poizan42/coreclr