merge-ort: prevent the_repository from coming back

merge-ort: prevent the_repository from coming back

Due to the use of DEFAULT_ABBREV, we cannot get rid of our usage of
USE_THE_REPOSITORY_VARIABLE.  However, we have removed all other uses of
the_repository in merge-ort a few times.  But they keep coming back.

Define the_repository to make it a compilation error so that they don't
come back any more.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>