builtin/rev-parse: fix memory leak with `--parseopt`

builtin/rev-parse: fix memory leak with `--parseopt`

The `--parseopt` mode allows shell scripts to have the same option
parsing mode as we have in C builtins. It soaks up a set of option
descriptions via stdin and massages them into proper `struct option`s
that we can then use to parse a set of arguments.

We only partially free those options when done though, creating a memory
leak. Interestingly, we only end up free'ing the first option's help,
which is of course wrong.

Fix this by freeing all option's help fields as well as their `argh`
fields to plug this memory leak.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>