remote: run "remote rm" argv through parse_options()

remote: run "remote rm" argv through parse_options()

The "git remote rm" command's option parsing is fairly primitive: it
insists on a single argument, which it treats as the remote name, and
displays a usage message otherwise.

This is OK, and maybe even convenient, as you could run:

  git remote rm --foo

to drop a remote named "--foo". But it's also weirdly unlike most of the
rest of Git, which would complain that there is no option "--foo". The
right way to spell it by our conventions is:

  git remote rm -- --foo

but this doesn't currently work.

So let's bring the command in line with the rest of Git (including its
sibling subcommands!) by feeding argv to parse_options(). We already
have an empty options array for the usage helper.

Note that we have to adjust the argc index down by one, as
parse_options() eats the program name from the start of the array.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>