stop zeroing exchange heap allocations and some other more minor allocations

I removed the unused wrappers methods named `calloc` because they relied on the malloc wrapper have a `bool zero = true` default parameter (which resulted in some accidental zeroing). Perhaps wrapping the actual calloc function would be useful, but I don't know of an existing use case that could switch to them from malloc so I just removed them.

This gives an ~1% performance improvement for TreeMap, which does a lot of small allocations. Vectors use `realloc` which didn't zero before these changes so there's no change in performance.