swift234

Drop the notion of "alias" names for CF types.

Previously we imported a Core Foundation type "CCFooRef" as "CCFoo",
but also provided a typealias "CCFooRef". In Swift 3, we decided to
mark "CCFooRef" unavailable to force developers to consistently use
"CCFoo". Now that we have infrastructure to mark /all/ renamed
declarations as unavailable, just use that to track the renaming,
i.e. pretend that "CCFooRef" was the "Swift 2" name for the type.

This doesn't change the conflict resolution behavior: if there's
another name "CCFoo" in the same module, the CF type will be
imported as just "CCFooRef".

Groundwork cleanup for rdar://problem/26347297, which notes that our
import-as-member fix-its use the "Ref" names rather than the short
names.