worktree: simplify incompatibility message for --orphan and commit-ish
Use a single translatable string to report that the worktree add option
--orphan is incompatible with a commit-ish instead of having the
commit-ish in a separate translatable string. This reduces the number
of strings to translate and gives translators the full context.
A similar message is used in builtin/describe.c, but with the plural of
commit-ish, and here we need the singular form.
Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>