create_notes_commit() is needed by both the notes-merge code, and by
commit_notes() in notes-utils. Since it is generally useful, and not
bound to the notes-merge machinery, we move it from (the more specific)
notes-merge to (the more general) notes-utils.
Signed-off-by: Johan Herland <johan@herland.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>