ObjC lifetime: pull sugar off when the qualifiers conflict.

It's possible to have multiple local ObjCLifetime qualifiers. When there is
a conflict, we can't stop after we reach a type that is directly qualified.
We need to keep pulling sugar off and removing the ObjCLifetime qualifers.

rdar://25804796

Differential Revision: http://reviews.llvm.org/D20843

llvm-svn: 271409