[Clang importer] Don't suppress properties due to async method imports.
The Clang importer had some logic to suppress the import of a property that
had the same name as a method with no parameters. This logic
inadvertently meant that an async import of a completion-handler method
could prevent a (non-async) property of the same name to not be
imported, breaking existing code. In such cases, don't suppress the
property import.
Fixes rdar://73326019.