contrib: simplify the genosxversion.py command to find the hg libraries
I forget what problem I ran into while trying to teach the makefile to use a
non-system python. (It might have ben missing hg-evolve and/or keyring, but
`check_output()` was raising an error.) This still isn't great because it will
return non zero for something like the username not being set, even though we
aren't asking for it. But I suppose it's still useful to simplify.
Differential Revision: https://phab.mercurial-scm.org/D6753
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}