sim: Automatically unregister probe listeners

The ProbeListener base class automatically registers itself with a
probe manager. Currently, the class does not unregister a itself when
it is destroyed, which makes removing probes listeners somewhat
cumbersome. This patch adds an automatic call to
manager->removeListener in the ProbeListener destructor, which solves
the problem.

src/sim/probe/probe.cc

@@ -62,11 +62,17 @@ ProbeListenerObject::~ProbeListenerObject()
     listeners.clear();
 }
 
-ProbeListener::ProbeListener(ProbeManager *manager, const std::string &name)
+ProbeListener::ProbeListener(ProbeManager *_manager, const std::string &_name)
+    : manager(_manager), name(_name)
 {
     manager->addListener(name, *this);
 }
 
+ProbeListener::~ProbeListener()
+{
+    manager->removeListener(name, *this);
+}
+
 ProbeListenerObject*
 ProbeListenerObjectParams::create()
 {

src/sim/probe/probe.hh

@@ -104,7 +104,11 @@ class ProbeListener
 {
   public:
     ProbeListener(ProbeManager *manager, const std::string &name);
-    virtual ~ProbeListener() {}
+    virtual ~ProbeListener();
+
+  protected:
+    ProbeManager *const manager;
+    const std::string name;
 };
 
 /**