Revert "Don't build invalid AST nodes during recovery"

This reverts commit r224451. It caused us to reject some valid existing
code.

This code appears to run in non-error cases as well as error cases. If
the scope of a DependentScopeDeclRefExpr is still incomplete it probably
means we still have more instantiation to do.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@224526 91177308-0d34-0410-b5e6-96231b3b80d8