clang_tidy: DCE and simplify

This patch contains a few things:

- We've synced to a fixed |warn.py|, so we can remove an old workaround.
- Our remaining call to clang_tidy_execute can apparently be replaced by
  a call to |subprocess.check_call|, which removes what is apparently
  our last use of clang_tidy_execute.
- This slightly restructures code to just |shutil.rmtree| instead of
  |os.remove|, since it lets us avoid try/except blocks with its
  |ignore_errors| param.

BUG=chromium:960495
TEST=llvm-clang-tidy-toolchain-tryjob

Change-Id: Ia7b20db03c884d244b15198c4c9995b5d1e71220
Reviewed-on: https://chromium-review.googlesource.com/1601198
Commit-Ready: George Burgess <gbiv@chromium.org>
Tested-by: George Burgess <gbiv@chromium.org>
Reviewed-by: Caroline Tice <cmtice@chromium.org>
2 files changed