ARM64: Nuke some dead code.

Missed in previous commit.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206343 91177308-0d34-0410-b5e6-96231b3b80d8
[ARM64,C++11] Tidy up branch relaxation a bit w/ c++11.

No functional change.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206344 91177308-0d34-0410-b5e6-96231b3b80d8