CONFIG_DEBUG_SLAB_LEAK has been removed, so remove it from defconfig.

Link: http://lkml.kernel.org/r/alpine.DEB.2.21.1905201015460.96074@chino.kir.corp.google.com
Fixes: 7878c231 ("slab: remove /proc/slab_allocators")
Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>