Slab: Remove fake slab

Slab: Remove fake slab

From the beginning, there is a years-old implementation of a slab
not actually being a slab, just transparently passing all requests
to malloc and free. We don't need that anymore, we have different
methods now to determine whether the problem is the allocator or
something else, and as we are going to change the slab API anyway,
together with some behavioral updates, having a fake slab is just
an anachronism.