Support for generating an rpm was dropped in ab214331cf ("Makefile: stop
pretending to support rpmbuild", 2016-04-04). We don't generate any
*.spec files so there is no need to clean them up.
Signed-off-by: Todd Zullinger <tmz@pobox.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>