Remove unused diagnostic.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@193774 91177308-0d34-0410-b5e6-96231b3b80d8
iboutletcollection really does have custom parsing.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@193777 91177308-0d34-0410-b5e6-96231b3b80d8