[arcmt] GC migrator: don't try to remove redundant __strong, it does
more harm than good.

Fixes rdar://10522805&10521433

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@151424 91177308-0d34-0410-b5e6-96231b3b80d8
7 files changed