Remove more dead code for emitting diagnostics. The callers of these

functions already precluded dependent types from reaching them.

Also change one of the callers to not error when a trait is applied to
a dependent type. This is a perfectly reasonable pattern, and both Unary
and Binary type traits already support dependent types (by populating
the AST with a nonce value).

Remove the actual diagnostic, since these aren't errors.

llvm-svn: 130651