btl/uct: add missing opal_mem_hooks_unregister_release call

This commit fixes a bug when using the UCT btl with the UCX memory
hooks disabled. We were misssing a call to
opal_mem_hooks_unregister_release to remove the btl memory hook
callback.

Signed-off-by: Nathan Hjelm <hjelmn@lanl.gov>
(cherry picked from commit 36c206d2d616578c97853d1d69727a1d6e165c1e)
Signed-off-by: Nathan Hjelm <hjelmn@lanl.gov>

opal/mca/btl/uct/btl_uct_module.c

@@ -288,6 +288,10 @@ int mca_btl_uct_finalize (mca_btl_base_module_t* btl)
     mca_btl_uct_endpoint_t *endpoint;
     uint64_t key;
 
+    if (mca_btl_uct_component.disable_ucx_memory_hooks) {
+        opal_mem_hooks_unregister_release (mca_btl_uct_mem_release_cb);
+    }
+
     /* clean up any leftover endpoints */
     OPAL_HASH_TABLE_FOREACH(key, uint64, endpoint, &uct_module->id_to_endpoint) {
         OBJ_RELEASE(endpoint);