builtin/{grep,log}.: don't define "USE_THE_INDEX_COMPATIBILITY_MACROS"

builtin/{grep,log}.: don't define "USE_THE_INDEX_COMPATIBILITY_MACROS"

Adding "USE_THE_INDEX_COMPATIBILITY_MACROS" to these two appears to
have been unnecessary from the start, as going back and compiling
f8adbec9fea (cache.h: flip NO_THE_INDEX_COMPATIBILITY_MACROS switch,
2019-01-24) without that addition works.

Let's not have these ask for the compatibility macros from cache.h
that they don't need.

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