Revert the allocate/free -> get/put change from jemalloc change

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().