git-submodule.sh: remove unused top-level "--branch" argument

In 5c08dbbdf1a (git-submodule: fix subcommand parser, 2008-01-15) the "--branch" option was supported as an option to "git submodule" itself, i.e. "git submodule --branch" as a side-effect of its implementation. Then in b57e8119e6e (submodule: teach set-branch subcommand, 2019-02-08) when the "set-branch" subcommand was added the assertion that we shouldn't have "--branch" anywhere except as an argument to "add" and "set-branch" was copy/pasted from the adjacent check for "--cache" added (or rather modified) in 496eeeb19b9 (git-submodule.sh: avoid "test <cond> -a/-o <cond>", 2014-06-10). But there's been a logic error in that check, which at a glance looked like it should be supporting: git submodule --branch <branch> (add | set-branch) [<options>] But due to "||" in the condition (as opposed to "&&" for "--cache") if we have "--branch" here already we'll emit usage, even for "add" and "set-branch". So in addition to never having documented this form, it hasn't worked since b57e8119e6e was released with v2.22.0. So it's safe to remove this code. I.e. we don't want to support the form noted above, but only: git submodule (add | set-branch) --branch <branch> [<options>] Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>