Cleanup: Remove github helper scripts.

Blink on github is not supported, Blink lives in:
chromium.googlesource.com/chromium/blink/+/master.

So these scripts are from an era where Chromium was integrating WebKit,
but since we forked and created Blink, they don't make much sense
anymore.

BUG=None
TEST=None
R=dpranke@chromium.org

Review URL: https://codereview.chromium.org/563983002

git-svn-id: svn://svn.chromium.org/blink/trunk@181956 bbb929c8-8fbe-4397-9dbb-9b2b20218538