Kill deprecated -fbounds-checking flag

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@204436 91177308-0d34-0410-b5e6-96231b3b80d8
Document removed flags in release notes

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@204438 91177308-0d34-0410-b5e6-96231b3b80d8