swift234

[Clang importer] Always pass an effective context to importDeclContextOf.

Some of the callers to importDeclContextOf could and should have
passed an effective context, but didn't, so (e.g.) an enum defined in
C couldn't be mapped to a nested type in Swift. Eliminate the
single-argument importDeclContextOf honeypot so we remember to pass
down the effective Clang context. Fixes rdar://problem/25502497.