builtin/update-server-info: remove the_repository global variable

builtin/update-server-info: remove the_repository global variable

Remove the_repository global variable in favor of the repository
argument that gets passed in "builtin/update-server-info.c".

When `-h` is passed to the command outside a Git repository, the
`run_builtin()` will call the `cmd_update_server_info()` function
with `repo` set to NULL and then early in the function, "parse_options()"
call will give the options help and exit, without having to consult much
of the configuration file. So it is safe to omit reading the config when
`repo` argument the caller gave us is NULL.

Mentored-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Usman Akinyemi <usmanakinyemi202@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>