cross/build-rootfs.sh: fix default UbuntuPackages for default BuildArch (#7644)
cross/build-rootfs.sh: fix default UbuntuPackages for default BuildArch (#7644)

* better default UbuntuPackages for default BuildArch
* Remove multiple sets of _UbuntuPackages to default

yizhang82/coreclr,JosephTremoulet/coreclr,sagood/coreclr,ruben-ayrapetyan/coreclr,gkhanna79/coreclr,alexperovich/coreclr,botaberg/coreclr,cshung/coreclr,krk/coreclr,Dmitry-Me/coreclr,wateret/coreclr,gkhanna79/coreclr,YongseopKim/coreclr,dasMulli/coreclr,mskvortsov/coreclr,alexperovich/coreclr,mmitche/coreclr,sagood/coreclr,sagood/coreclr,krytarowski/coreclr,poizan42/coreclr,James-Ko/coreclr,pgavlin/coreclr,cshung/coreclr,jamesqo/coreclr,pgavlin/coreclr,JonHanna/coreclr,AlexGhiondea/coreclr,wateret/coreclr,YongseopKim/coreclr,JosephTremoulet/coreclr,mskvortsov/coreclr,poizan42/coreclr,russellhadley/coreclr,rartemev/coreclr,cmckinsey/coreclr,pgavlin/coreclr,AlexGhiondea/coreclr,yeaicc/coreclr,dasMulli/coreclr,kyulee1/coreclr,AlexGhiondea/coreclr,mskvortsov/coreclr,mskvortsov/coreclr,krk/coreclr,neurospeech/coreclr,botaberg/coreclr,wateret/coreclr,qiudesong/coreclr,kyulee1/coreclr,yizhang82/coreclr,wtgodbe/coreclr,cshung/coreclr,cshung/coreclr,cmckinsey/coreclr,neurospeech/coreclr,cydhaselton/coreclr,dasMulli/coreclr,krk/coreclr,krytarowski/coreclr,krytarowski/coreclr,jamesqo/coreclr,tijoytom/coreclr,rartemev/coreclr,botaberg/coreclr,cshung/coreclr,wateret/coreclr,ragmani/coreclr,parjong/coreclr,krk/coreclr,krytarowski/coreclr,YongseopKim/coreclr,qiudesong/coreclr,yeaicc/coreclr,botaberg/coreclr,gkhanna79/coreclr,yeaicc/coreclr,hseok-oh/coreclr,alexperovich/coreclr,cmckinsey/coreclr,neurospeech/coreclr,kyulee1/coreclr,pgavlin/coreclr,yeaicc/coreclr,dpodder/coreclr,mskvortsov/coreclr,tijoytom/coreclr,kyulee1/coreclr,tijoytom/coreclr,yeaicc/coreclr,rartemev/coreclr,JosephTremoulet/coreclr,yeaicc/coreclr,sagood/coreclr,qiudesong/coreclr,dpodder/coreclr,tijoytom/coreclr,sagood/coreclr,mmitche/coreclr,yeaicc/coreclr,jamesqo/coreclr,cydhaselton/coreclr,James-Ko/coreclr,tijoytom/coreclr,Dmitry-Me/coreclr,dasMulli/coreclr,dpodder/coreclr,cmckinsey/coreclr,qiudesong/coreclr,wtgodbe/coreclr,dasMulli/coreclr,dpodder/coreclr,ruben-ayrapetyan/coreclr,mmitche/coreclr,yizhang82/coreclr,AlexGhiondea/coreclr,gkhanna79/coreclr,James-Ko/coreclr,hseok-oh/coreclr,hseok-oh/coreclr,poizan42/coreclr,sjsinju/coreclr,russellhadley/coreclr,ruben-ayrapetyan/coreclr,yizhang82/coreclr,wtgodbe/coreclr,jamesqo/coreclr,krk/coreclr,Dmitry-Me/coreclr,parjong/coreclr,hseok-oh/coreclr,alexperovich/coreclr,pgavlin/coreclr,James-Ko/coreclr,cmckinsey/coreclr,poizan42/coreclr,dpodder/coreclr,alexperovich/coreclr,gkhanna79/coreclr,botaberg/coreclr,cshung/coreclr,parjong/coreclr,ruben-ayrapetyan/coreclr,jamesqo/coreclr,YongseopKim/coreclr,alexperovich/coreclr,botaberg/coreclr,dpodder/coreclr,sagood/coreclr,Dmitry-Me/coreclr,hseok-oh/coreclr,wateret/coreclr,sjsinju/coreclr,yizhang82/coreclr,cydhaselton/coreclr,AlexGhiondea/coreclr,James-Ko/coreclr,rartemev/coreclr,YongseopKim/coreclr,JonHanna/coreclr,JonHanna/coreclr,poizan42/coreclr,sjsinju/coreclr,gkhanna79/coreclr,ragmani/coreclr,mmitche/coreclr,pgavlin/coreclr,qiudesong/coreclr,rartemev/coreclr,parjong/coreclr,JosephTremoulet/coreclr,russellhadley/coreclr,neurospeech/coreclr,JonHanna/coreclr,Dmitry-Me/coreclr,krytarowski/coreclr,James-Ko/coreclr,mskvortsov/coreclr,neurospeech/coreclr,ragmani/coreclr,ragmani/coreclr,hseok-oh/coreclr,sjsinju/coreclr,russellhadley/coreclr,mmitche/coreclr,JonHanna/coreclr,Dmitry-Me/coreclr,wtgodbe/coreclr,kyulee1/coreclr,sjsinju/coreclr,dasMulli/coreclr,russellhadley/coreclr,cydhaselton/coreclr,cydhaselton/coreclr,krk/coreclr,tijoytom/coreclr,sjsinju/coreclr,AlexGhiondea/coreclr,jamesqo/coreclr,wtgodbe/coreclr,JosephTremoulet/coreclr,ragmani/coreclr,poizan42/coreclr,mmitche/coreclr,ragmani/coreclr,YongseopKim/coreclr,ruben-ayrapetyan/coreclr,kyulee1/coreclr,rartemev/coreclr,cmckinsey/coreclr,cmckinsey/coreclr,krytarowski/coreclr,JosephTremoulet/coreclr,ruben-ayrapetyan/coreclr,cydhaselton/coreclr,parjong/coreclr,JonHanna/coreclr,dasMulli/coreclr,Dmitry-Me/coreclr,wateret/coreclr,neurospeech/coreclr,parjong/coreclr,qiudesong/coreclr,russellhadley/coreclr,yizhang82/coreclr,wtgodbe/coreclr