repository: drop `the_index` variable
All users of `the_index` have been converted to use either a custom
`struct index_state *` or the index provided by `the_repository`. We can
thus drop the globally-accessible declaration of this variable. In fact,
we can go further than that and drop `the_index` completely now and have
it be allocated dynamically in `initialize_repository()` as all the
other data structures in it are.
This concludes the quest to make Git `the_index` free, which has started
with
4aab5b46f4 (Make read-cache.c "the_index" free., 2007-04-01).
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>