mm: kmemleak: drop kmemleak_warning variable

mm: kmemleak: drop kmemleak_warning variable

These are a trivial mm/kmemleak.c cleanups.  I found these while reading
through the code.

This patch (of 3):

The kmemleak_warning variable is not used since commit c5665868183f ("mm:
kmemleak: use the memory pool for early allocations"), drop it.

Link: https://lkml.kernel.org/r/cover.1746046744.git.luizcap@redhat.com
Link: https://lkml.kernel.org/r/97e23faa7b67099027a1094c9438da5f72e037af.1746046744.git.luizcap@redhat.com
Signed-off-by: Luiz Capitulino <luizcap@redhat.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>