Since c99f069 (bisect--helper: remove "--next-vars" option as it is
now useless - 2009-04-21), this flag has always been off. Remove the
flag and all related code.
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>