Makefile: drop unneeded indirection for GIT-VERSION-GEN outputs

Makefile: drop unneeded indirection for GIT-VERSION-GEN outputs

Some of the callsites of GIT-VERSION-GEN generate the target file with a
"+" suffix first and then move the file into place when the new contents
are different compared to the old contents. This allows us to avoid a
needless rebuild by not updating timestamps of the target file when its
contents will remain unchanged anyway.

In fact though, this exact logic is already handled in GIT-VERSION-GEN,
so doing this manually is pointless. This is a leftover from an earlier
version of 4838deab65 (Makefile: refactor GIT-VERSION-GEN to be
reusable, 2024-12-06), where the script didn't handle that logic for us.

Drop the needless indirection.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>