Move python-phabricator to a 'real' subrepo as well.

Summary:
I missed this when I moved phabricator/arcanist/libphutil to being
'real' subrepos rather than fake ones.

Test Plan: ls python-phabricator and it looks correct.

Reviewers: benkomalo, alpert

Reviewed By: alpert

Differential Revision: http://phabricator.khanacademy.org/D8481