lib: remove unused msg parameter in debug_agent

Removed the msg parameter in the Client function
of _debug_agent.js, because it is unused.

lib/_debug_agent.js

@@ -108,7 +108,7 @@ function Client(agent, socket) {
 }
 util.inherits(Client, Transform);
 
-Client.prototype.destroy = function destroy(msg) {
+Client.prototype.destroy = function destroy() {
   this.socket.destroy();
 
   this.emit('close');