Revert "Add Chrono.h - std::chrono support header"

This reverts commit r284590 as it fails on the mingw buildbot. I think I know the
fix, but I cannot test it right now. Will reapply when I verify it works ok.

This reverts r284590.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@284615 91177308-0d34-0410-b5e6-96231b3b80d8
10 files changed