Makefile: drop -DSUPPRESS_ANNOTATED_LEAKS

Makefile: drop -DSUPPRESS_ANNOTATED_LEAKS

The -DSUPPRESS_ANNOTATED_LEAKS preprocessor directive was used to enable
our `UNLEAK()` macro in the past, which marks memory as still-reachable
so that the leak sanitizer does not complain. Starting with 52c7dbd036
(git-compat-util: drop now-unused `UNLEAK()` macro, 2024-11-20) this
macro has been removed, and thus the preprocessor directive is not
required anymore, either.

Drop it.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>