git-p4: use 'git hook' to run hooks

git-p4: use 'git hook' to run hooks

Instead of duplicating the behavior of run-command.h:run_hook_le() in
Python, we can directly call 'git hook run'. We emulate the existence
check with the --ignore-missing flag.

We're dropping the "verbose" handling added in 9f59ca4d6af (git-p4:
create new function run_git_hook, 2020-02-11), those who want
diagnostic output about how hooks are run are now able to get that via
e.g. the trace2 facility and GIT_TRACE=1.

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