cpu: delete listener ptrs after removal

The listener pointer does not get deleted with the removeListener()
function call, so we need to make sure it is deleted in the
ProbeListenerObject.

Change-Id: I370f34651b889c8c00a378743e9c1c09fa1d775e

src/cpu/probes/inst_tracker.cc

@@ -63,13 +63,18 @@ LocalInstTracker::stopListening()
 {
     ifListening = false;
     bool _ifRemoved;
-    for (auto &listener : listeners) {
+    for (auto &_listener : listeners) {
         _ifRemoved = getProbeManager()->removeListener(
             "RetiredInsts",
-            *listener
+            *_listener
         );
-        DPRINTF(InstTracker, "If removed: %s\n", _ifRemoved ? "Yes" : "No");
+        panic_if(!_ifRemoved, "Failed to remove listener");
+        if (_listener != nullptr) {
+            delete(_listener);
+            DPRINTF(InstTracker, "Deleted Listener pointer\n");
+        }
     }
+    DPRINTF(InstTracker, "Stop listening to RetiredInsts\n");
 }