Fix login breakage when merging accounts on iOS.
Revert "WIP"

This reverts commit cd6b029fbecd9dd7f61ccde4cb42f2024337d4e7.
Fix iOS-only classes to use new threading methods

Change-Id: I5349bf482fa1da66e66b7f091b7d84962d57eecd
Rename dispatch_libspotify_async to SPDispatchAsync.

Change-Id: If5ca9473d6f9ddb1c6a004b797e201243f3ae6c7