Make git cache delete a defunct directory instead of moving it

So the original intention of moving it to a different directory to be deleted later
was to (1) save it for diagnosis (2) be a single inode swap rather than a long
rmtree delete.

1. No one is actually looking at these directories
2. The tmpdir sometimes end up on a different partition, so it ends up being
   a copy + delete instead.  Since we're not getting timeouts from that, its
   probably actually better to just straight up delete it.

BUG=410727

Review URL: https://codereview.chromium.org/538993002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@291818 0039d316-1c4b-4281-b951-d872f2087c98

git_cache.py

@@ -14,7 +14,6 @@ import re
 import tempfile
 import threading
 import time
-import shutil
 import subprocess
 import sys
 import urlparse
@@ -344,13 +343,6 @@ class Mirror(object):
       bootstrapped = not depth and bootstrap and self.bootstrap_repo(tempdir)
       if bootstrapped:
         # Bootstrap succeeded; delete previous cache, if any.
-        try:
-          # Try to move folder to tempdir if possible.
-          defunct_dir = tempfile.mkdtemp()
-          shutil.move(self.mirror_path, defunct_dir)
-          self.print('Moved defunct directory for repository %s from %s to %s'
-                     % (self.url, self.mirror_path, defunct_dir))
-        except Exception:
         gclient_utils.rmtree(self.mirror_path)
       elif not os.path.exists(config_file):
         # Bootstrap failed, no previous cache; start with a bare git dir.