[CSM] Remove on_connect callback (#6941)

Fixes #6939

src/script/cpp_api/s_client.h

@@ -40,8 +40,6 @@ class ScriptApiClient : virtual public ScriptApiBase
 	// Calls on_shutdown handlers
 	void on_shutdown();
 
-	void on_connect();
-
 	// Chat message handlers
 	bool on_sending_message(const std::string &message);
 	bool on_receiving_message(const std::string &message);