push: use die_for_incompatible_opt4() for - -delete/--tags/--all/--mirror

push: use die_for_incompatible_opt4() for - -delete/--tags/--all/--mirror

The push option --delete is incompatible with --all, --mirror, and
--tags; --tags is incompatible with --all and --mirror; --all is
incompatible with --mirror.  This means they are all incompatible with
each other.  And --branches is an alias for --all.

Use the function for checking four mutually incompatible options,
die_for_incompatible_opt4(), to perform this check in one place and
without repetition.  This is shorter and clearer.

Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>