Revert the allocate/free -> get/put change from jemalloc change
In the jemalloc merge request, we missed the fact that ah_frees and ah_handles are reallocated which is not compatible with using isc_mem_get() for allocation and isc_mem_put() for deallocation. This commit reverts that part and restores use of isc_mem_allocate() and isc_mem_free().
Closes #2812 (closed)