tests/unwrap-message-id.py

tests: replace some `python` by `"$PYTHON"` to not only use Python 2

I deleted my `python` binary as a test and a few tests started
failing.

Differential Revision: https://phab.mercurial-scm.org/D10250

from __future__ import absolute_import, print_function

import sys

for line in sys.stdin:
    if line.lower() in ("message-id: \n", "in-reply-to: \n"):
        line = line[:-2]
    print(line, end="")