Codechange: remove pointless close call due to resolving virtual functions statically in destructors

In the destructors of many of the network related classes Close() is called, just like the
top class in that hierarchy. However, due to virtual functions getting resolved statically
in the destructor it would always call the empty Close() of the top class.
Document the other cases where a virtual call is resolved statically.

src/network/core/core.h

@@ -46,10 +46,7 @@ public:
 	NetworkSocketHandler() { this->has_quit = false; }
 
 	/** Close the socket when destructing the socket handler */
-	virtual ~NetworkSocketHandler() { this->Close(); }
-
-	/** Really close the socket */
-	virtual void Close() {}
+	virtual ~NetworkSocketHandler() {}
 
 	/**
 	 * Close the current connection; for TCP this will be mostly equivalent