[BUILDBOT] Remove local python-phabricator dependency

Summary:
The bugfix patch (https://github.com/disqus/python-phabricator/pull/62)
has been released with version 0.8.0. There is no need for keeping our
local patched version anymore.

Test Plan:

pytest

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D9305