Remove racy and unneeded CleanupCacheDir() calls.

The simple cache tests don't need to cleanup cache dir
after dooming the entire cache; in fact it causes races with
index creation.

R=pasko@chromium.org, clamy@chromium.org
BUG=333527

Review URL: https://codereview.chromium.org/136563003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244889 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 244889