util: Remove support for hg patches in patch creation script

util: Remove support for hg patches in patch creation script

Simplify the patch creation helper script by removing support for
automatic conversion to Mercurial's patch format. We no longer use
Mercurial as a primary repository, so this support is not likely to be
needed again.

Change-Id: I83f6efb9ccaee9c548b33257a4d6128153750c76
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Curtis Dunham <curtis.dunham@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/5162
Reviewed-by: Gabe Black <gabeblack@google.com>