bisect--helper: convert `vocab_*` char pointers to char arrays
Instead of using a pointer that points at a constant string,
just give name directly to the constant string; this way, we
do not have to allocate a pointer variable in addition to
the string we want to use.
Let's convert `vocab_bad` and `vocab_good` char pointers to char arrays.
Mentored-by: Christian Couder <chriscool@tuxfamily.org> Signed-off-by: Miriam Rubio <mirucam@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>