swift234

[serialization] Stop eagerly deserializing decls with conversion functions.

There shouldn't ever be a reason to do this: if a conversion function is
ever selected by the type-checker, it's because the type the conversion
lives on was suggested by another constraint, which means we can do a
normal lookup for the conversion function.

This is actually the only thing being eagerly deserialized, so remove the
notion of eager deserialization altogether.

Swift SVN r11220