With 77b9b1d (add_to_alternates_file: don't add duplicate entries,
2015-08-10) the last caller of function "hold_lock_file_for_append"
has been removed, so we can remove the function as well.
Signed-off-by: Ralf Thielow <ralf.thielow@gmail.com> Acked-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>