docs(input): remove deprecated isolated scope pitfall
docs(input): remove deprecated isolated scope pitfall

The 1.2 release fixed the documented pitfall at a26703296f34a82d0447248e38fc0403c2bafbe7
by isolating only the isolated directive's scope.

Closes #5179

ggershoni/angular.js,ggershoni/angular.js,ggershoni/angular.js,ggershoni/angular.js