Removed dead code from ObjCARCOpts relating to tracking objc_retainBlocks through the ARC Dataflow analysis. By the time we get to the ARC dataflow analysis, any objc_retainBlock calls are not optimizable.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178306 91177308-0d34-0410-b5e6-96231b3b80d8