### Godot version

master

### System information

Ubuntu

### Issue description

I think one of the recent changes wrapped the project converter in `#ifndef DISABLE_DEPRECATED` but missed the coresponding code in `main.cpp` (and potentially other places).
```
main/main.cpp: In static member function 'static bool Main::start()':
main/main.cpp:2551:33: error: 'ProjectConverter3To4' was not declared in this scope
 2551 |                 int exit_code = ProjectConverter3To4(converter_max_kb_file, converter_max_line_length).convert();
      |                                 ^~~~~~~~~~~~~~~~~~~~
main/main.cpp:2556:33: error: 'ProjectConverter3To4' was not declared in this scope
 2556 |                 int exit_code = ProjectConverter3To4(converter_max_kb_file, converter_max_line_length).validate_conversion();
```

### Steps to reproduce

for instance, try to compile with `deprecated = "no"` in your `custom.py`.

### Minimal reproduction project

n/a
memdelete(time_singleton);
	}
	if (translation_server) {
		memdelete(translation_server);
	}
	if (globals) {
		memdelete(globals);
	}
	if (engine) {
		memdelete(engine);
	}
	if (packed_data) {
		memdelete(packed_data);
	}
	if (file_access_network_client) {
		memdelete(file_access_network_client);
	}
	unregister_core_driver_types();
	unregister_core_extensions();
	unregister_core_types();
	OS::get_singleton()->_cmdline.clear();
	OS::get_singleton()->_user_args.clear();
	if (message_queue) {
		memdelete(message_queue);
	}
	OS::get_singleton()->finalize_core();
	locale = String();
	return exit_code;
}
Error Main::setup2(Thread::ID p_main_tid_override) {