Revert "Clang build.py, set shell=True in GetCommitDescription"

This reverts commit 69f5d986.

Breaks bots: https://logs.chromium.org/logs/chromium/buildbucket/cr-buildbucket.appspot.com/8867785886893833968/+/steps/gclient_runhooks/0/stdout

Change-Id: Ic5c2bed98840e5d1cc2543bcdad5790a1ac82d57
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2439437
Auto-Submit: Arthur Eubanks <aeubanks@google.com>
Commit-Queue: Hans Wennborg <hans@chromium.org>
Reviewed-by: Hans Wennborg <hans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#812021}

tools/clang/scripts/build.py

@@ -176,7 +176,7 @@ def GetCommitDescription(commit):
 
   Needs to be called from inside the git repository dir."""
   return subprocess.check_output(
-      ['git', 'describe', '--long', '--abbrev=8', commit], shell=True).rstrip()
+      ['git', 'describe', '--long', '--abbrev=8', commit]).rstrip()
 
 
 def DeleteChromeToolsShim():