Revert "CLANG: Workaround for violations on unsupported command -mtune=cortex-a15"
Useless. Is already set in build at:
https://github.com/VanirAOSP/build/commit/0e524e1a703d79cb1422d6a8d1ae7a774d65d08d
This reverts commit 60398f1d5c212fd43ba98d76c9a21980131ca10b.

Change-Id: I0d87d473172de3776e5fef919fb5a41b6338bf5f