Inspector: replace generic discardAgents logic with explicit call to discard a listener.

Source/core/inspector/InspectorBaseAgent.h

Index: Source/core/inspector/InspectorBaseAgent.h
diff --git a/Source/core/inspector/InspectorBaseAgent.h b/Source/core/inspector/InspectorBaseAgent.h
index 75bd7b4cbfd193b2bf23547a0d552cb24188cbc1..ed36b568df9cbc25685108e0b6c1f839424d6151 100644
--- a/Source/core/inspector/InspectorBaseAgent.h
+++ b/Source/core/inspector/InspectorBaseAgent.h
@@ -52,7 +52,6 @@ public:
     virtual void clearFrontend() { }
     virtual void restore() { }
     virtual void registerInDispatcher(InspectorBackendDispatcher*) = 0;
-    virtual void discardAgent() { }
 
     String name() { return m_name; }
 
@@ -74,7 +73,6 @@ public:
     void clearFrontend();
     void restore();
     void registerInDispatcher(InspectorBackendDispatcher*);
-    void discardAgents();
 
 private:
     Vector<OwnPtr<InspectorBaseAgentInterface> > m_agents;