Merge branch 'jk/drop-hg-to-git'

Remove an ancient and not well maintained Hg-to-git migration
script from contrib/.

Acked-by: Stelian Pop <stelian@popies.net>
cf. <37e4cd61-b370-437e-bd42-f98f47d3ad32@popies.net>

* jk/drop-hg-to-git:
  contrib: drop hg-to-git script

Author: gitster