maint: remove build-aux/git-version-gen.
maint: remove build-aux/git-version-gen.

* build-aux/git-version-gen: Remove.  This script conflicts with
the way mkrockspecs expects versions to be formatted.

Signed-off-by: Gary V. Vaughan <f9023000f29773649f3850298becb9544b5fd6a9@gnu.org>

gvvaughan/slingshot