6532f3740b ("completion: allow to customize the completable command
list", 2018-05-20) added the completion.commands config variable.
Multiple commands may be added or removed, separated by a space.
Demonstrate the failure of multiple removals.
Signed-off-by: Todd Zullinger <tmz@pobox.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>