Makefile: drop support for curl < 7.9.8 (again)

Makefile: drop support for curl < 7.9.8 (again)

In 1119a15b5c8 (http: drop support for curl < 7.11.1, 2021-07-30)
support for curl versions older than 7.11.1 was removed, and we
currently require at least version 7.19.4, see 644de29e220 (http: drop
support for curl < 7.19.4, 2021-07-30).

In those changes this Makefile-specific check added in
0890098780f (Decide whether to build http-push in the Makefile,
2005-11-18) was missed, now that we're never going to use such an
ancient curl version we don't need to check that we have at least
7.9.8 here. I have no idea what in http-push.c broke on versions older
than that.

This does not impact "NO_CURL" setups, as this is in the "else" branch
after that check.

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