Remove WebKit bugzilla/git support from my_activity.py

Tens of crickets suddenly cried out, and were suddenly silenced.

R=cjhopman@chromium.org, cmp@chromium.org, enne@chromium.org, cjhopman, cmp, enne, szager

Review URL: https://codereview.chromium.org/137373004

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@246193 0039d316-1c4b-4281-b951-d872f2087c98