parse-options: drop leading space from '--git-completion-helper' output

The output of 'git <cmd> --git-completion-helper' always starts with a space, e.g.: $ git config --git-completion-helper --global --system --local [...] This doesn't matter for the completion script, because field splitting discards that space anyway. However, later patches in this series will teach parse-options to handle subcommands, and subcommands will be included in the completion helper output as well. This will make the loop printing options (and subcommands) a tad more complex, so I wanted to test the result. The test would have to account for the presence of that leading space, which bugged my OCD, so let's get rid of it. Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>