bug#6513: bug#7171: vc-mtn to use "mtn automate"

[Lars Ingebrigtsen]

There's apparently not been any development on Monotone since 2014:

  https://www.monotone.ca/

According to this bug report, our vc-mtn doesn't work at all with the
version that was current in 2010, and there's been zero bug reports
about that in a decade.  So I think we should obsolete vc-mtn.el.

Does anybody have any comments?

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no