Time to cleanup the beta version note in the top level README.md
Time to cleanup the beta version note in the top level README.md

PiperOrigin-RevId: 212059835

chalin/angular2,chalin/angular2,matanlurey/angular,matanlurey/angular,matanlurey/angular,angulardart/angular,angulardart/angular,chalin/angular2,angulardart/angular