parse-options: remove PARSE_OPT_NEGHELP

parse-options: remove PARSE_OPT_NEGHELP

PARSE_OPT_NEGHELP is confusing because short options defined with that
flag do the opposite of what the helptext says. It is also not needed
anymore now that options starting with no- can be negated by removing
that prefix. Convert its only two users to OPT_NEGBIT() and OPT_BOOL()
and then remove support for PARSE_OPT_NEGHELP.

Signed-off-by: Rene Scharfe <redacted>
Acked-by: Jeff King <redacted>
Signed-off-by: Junio C Hamano <redacted>