revisions API users: use release_revisions() in http-push.c

revisions API users: use release_revisions() in http-push.c

In the case of cmd_main() in http-push.c we need to move the
deceleration of the "struct rev-list" into the loop over the
"remote_refs" when adding a release_revisions().

We'd previously set up the "revs" for each remote, but would
potentially leak memory on each one.

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