Remove rebaseline logic from GOM

It's dead.  The auto rebaseline bot won.

BUG=389681
R=abarth@chromium.org, abarth, dpranke

Review URL: https://codereview.chromium.org/358173003

git-svn-id: svn://svn.chromium.org/blink/trunk@177137 bbb929c8-8fbe-4397-9dbb-9b2b20218538