Makefile: remove $(GIT_VERSION) from $(SCRIPT_DEFINES)

Makefile: remove $(GIT_VERSION) from $(SCRIPT_DEFINES)

Remove the $(GIT_VERSION) from $(SCRIPT_DEFINES). Now every time HEAD
changes in a development copy we don't need to re-build the scripts
and script libraries.

This has not been needed since 2b9391bc675 (Makefile: do not replace
@@GIT_VERSION@@ in shell scripts, 2012-06-20). On my setup this
changes the re-making of 44 targets in a development copy where moved
HEAD to 27.

The $(GIT_VERSION) was seemingly left here by mistake or omission. We
didn't need it since 2b9391bc675, but in the later
e4dd89ab984 (Makefile: update scripts when build-time parameters
change, 2012-06-20) it was added to SCRIPT_DEFINES.

The two were part of the same series of patches, and given the summary
in [1] and [2] it looks like this was probably a case of some earlier
version of a later patch being combined with an updated earlier patch.

1. https://lore.kernel.org/git/20120619232231.GA6328@sigill.intra.peff.net/
2. https://lore.kernel.org/git/20120619232453.GB6496@sigill.intra.peff.net/

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>