swift234

[Sema] Don't validate decls that conform to known protocols ahead of time.

This is left over from the days where anyone can provide a literal type that
the type checker might go try if there's not enough context. Nowadays we just
use the default literal type and then give up. Therefore, let's do (a bit)
less work for each source file!

No user-visible functionality change. This will probably only really affect
the standard library compile, and even then only slightly.

Swift SVN r22663