tests/helper-killhook.py

test: disable test-subrepo-git.t in python2 + chg

I am a couple of days in try to debug that at it seems minor enough with enough
other priority to simply disable it for now.

Differential Revision: https://phab.mercurial-scm.org/D11253

import os


def killme(ui, repo, hooktype, **wkargs):
    os._exit(80)