The 'RemoveDirectory()' function in gclient_utils is deprecated and
rmtree() should be used instead for consistency.

This patch modifies all clients in depot_tools to use rmtree() instead
and removes the RemoveDirectory function.

+ The SVNWrapperTestCase.testRevertNoDotSvn() mocking
  expectation has been slightly changed. This was required
  because the test invokes code that used to call
  gclient_utils.RemoveDirectory() directly, while only
  gclient_utils.rmtree() was mocked.

BUG=NONE
R=maruel@chromium.org, ilevy@chromium.org
TEST=manually run gclient_utils_test / gclient_smoketest / scm_unittest / gclient_scm_test

Review URL: https://chromiumcodereview.appspot.com/14134010

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@196133 0039d316-1c4b-4281-b951-d872f2087c98