llvm_tools: migrate nightly_revert_checker to get_llvm_hash

Yay for replacing old custom logic

BUG=b:333462347
TEST=Unittests

Change-Id: I5459942eaaa08f0b0d694dff707bf34ee8ffe8b4
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/toolchain-utils/+/5454856
Commit-Queue: George Burgess <gbiv@chromium.org>
Tested-by: George Burgess <gbiv@chromium.org>
Reviewed-by: Bob Haarman <inglorion@chromium.org>
2 files changed