After introducing the stack handler in the previous commit,
we now have very similar code to the custom handler in test_mempool.c,
which creates a custom mempool based on simple mallocs.
The stack handler is a cleaner example of adding a new mempool handler,
so this commit replaces the custom handler test with a stack
handler test, and removes the custom handler code.

Signed-off-by: David Hunt <redacted>

[...]

-static struct rte_mempool_ops mempool_ops_custom = {
-	.name = "custom_handler",
-	.alloc = custom_mempool_alloc,
-	.free = custom_mempool_free,
-	.enqueue = custom_mempool_enqueue,
-	.dequeue = custom_mempool_dequeue,
-	.get_count = custom_mempool_get_count,
-};
-
-MEMPOOL_REGISTER_OPS(mempool_ops_custom);
-
-/*
  * save the object number in the first 4 bytes of object data. All
  * other bytes are set to 0.
  */

@@ -600,6 +507,7 @@ test_mempool(void)
 	struct rte_mempool *mp_cache = NULL;
 	struct rte_mempool *mp_nocache = NULL;
 	struct rte_mempool *mp_ext = NULL;