ObjectiveC. Remove warning diagnostic which checks

ObjectiveC. Remove warning diagnostic which checks
attribute on method declaration and implementation
match. This makes no sense. Most annotations are
meant for declarations only and one is for implementation.
This has been constant source of regresions and hackery to
get around special cases. I am removing this check.
Such checks must be done on a case by case basis and
when it makes sense. For example, it makes sense
for availability/deprecated and I will file a radar
for that. // rdar://15531984

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@195524 91177308-0d34-0410-b5e6-96231b3b80d8