### 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
break;
		}
	}
	
	{
		GLOBAL_DEF_RST_NOVAL("input_devices/pen_tablet/driver", "");
		GLOBAL_DEF_RST_NOVAL(PropertyInfo(Variant::STRING, "input_devices/pen_tablet/driver.windows", PROPERTY_HINT_ENUM, "wintab,winink"), "");
	}
	if (tablet_driver.is_empty()) { 
		tablet_driver = GLOBAL_GET("input_devices/pen_tablet/driver");
		if (tablet_driver.is_empty()) {
			tablet_driver = DisplayServer::get_singleton()->tablet_get_driver_name(0);
		}
	}
	for (int i = 0; i < DisplayServer::get_singleton()->tablet_get_driver_count(); i++) {
		if (tablet_driver == DisplayServer::get_singleton()->tablet_get_driver_name(i)) {
			DisplayServer::get_singleton()->tablet_set_current_driver(DisplayServer::get_singleton()->tablet_get_driver_name(i));
			break;
		}
	}
	if (DisplayServer::get_singleton()->tablet_get_current_driver().is_empty()) {
		DisplayServer::get_singleton()->tablet_set_current_driver(DisplayServer::get_singleton()->tablet_get_driver_name(0));
	}
	print_verbose("Using \"" + tablet_driver + "\" pen tablet driver...");
	
	rendering_server = memnew(RenderingServerDefault(OS::get_singleton()->get_render_thread_mode() == OS::RENDER_SEPARATE_THREAD));
	rendering_server->init();
	
	rendering_server->set_render_loop_enabled(!disable_render_loop);
	if (profile_gpu || (!editor && bool(GLOBAL_GET("debug/settings/stdout/print_gpu_profile")))) {