Remove the special-sauce malloc implementation?

[FredrikLindgren]

Elkhound et al. is normally linked with the no-op implementation smbase/malloc_stub.c of ckheap.h. Supposedly smbase/malloc.c (conventional and/or customised malloc + ckheap) is good for testing, or something, but a comment in smbase/Makefile.in describes it as being non-functional on Cygwin and OS X.

Given that the default is no-op, it should be safe to remove the lot of it (ckheap.h, malloc.c, malloc_stub.c, testmalloc.c and tmalloc.c) if there is no compelling reason for retaining the special-sauce implementation.