gclient on bots: don't cleanup lock files.

bot_update & gclient on bots instruct git cache locks
to be ignored, so there is no need to clean them up.

R=hinoka@chromium.org

Change-Id: I81c52cfcd44a42d13b641847439ac92053a7bc98
Reviewed-on: https://chromium-review.googlesource.com/791652
Reviewed-by: Ryan Tseng <hinoka@chromium.org>
Commit-Queue: Andrii Shyshkalov <tandrii@chromium.org>

gclient.py

@@ -1330,10 +1330,7 @@ it or fix the checkout.
     if cache_dir:
       cache_dir = os.path.join(self.root_dir, cache_dir)
       cache_dir = os.path.abspath(cache_dir)
-      # If running on a bot, force break any stale git cache locks.
-      if os.path.exists(cache_dir) and os.environ.get('CHROME_HEADLESS'):
-        subprocess2.check_call(['git', 'cache', 'unlock', '--cache-dir',
-                                cache_dir, '--force', '--all'])
+
     gclient_scm.GitWrapper.cache_dir = cache_dir
     git_cache.Mirror.SetCachePath(cache_dir)