cocci & cache.h: remove "USE_THE_INDEX_COMPATIBILITY_MACROS"

cocci & cache.h: remove "USE_THE_INDEX_COMPATIBILITY_MACROS"

Have the last users of "USE_THE_INDEX_COMPATIBILITY_MACROS" use the
underlying *_index() variants instead. Now all previous users of
"USE_THE_INDEX_COMPATIBILITY_MACROS" have been migrated away from the
wrapper macros, and if applicable to use the "USE_THE_INDEX_VARIABLE"
added in [1].

Let's leave the "index-compatibility.cocci" in place, even though it
won't be doing anything on "master". It will benefit any out-of-tree
code that need to use these compatibility macros. We can eventually
remove it.

1. bdafeae0b9c (cache.h & test-tool.h: add & use
   "USE_THE_INDEX_VARIABLE", 2022-11-19)

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>