Remove unnecessary virtual keyword occurrences

This makes it convenient to 'grep virtual' and 'grep override' :)

modules/missingmotd.cpp

@@ -20,7 +20,7 @@ class CMissingMotd : public CModule {
 public:
 	MODCONSTRUCTOR(CMissingMotd) {}
 
-	virtual void OnClientLogin() override {
+	void OnClientLogin() override {
 		PutUser(":irc.znc.in 422 :MOTD File is missing");
 	}
 };