### 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
initialize_modules(MODULE_INITIALIZATION_LEVEL_CORE);
	register_core_extensions();
	register_core_singletons();
	
	register_server_types();
	XRServer::set_xr_mode(XRServer::XRMODE_OFF); 
	initialize_modules(MODULE_INITIALIZATION_LEVEL_SERVERS);
	GDExtensionManager::get_singleton()->initialize_extensions(GDExtension::INITIALIZATION_LEVEL_SERVERS);
	translation_server->setup(); 
	if (!locale.is_empty()) {
		translation_server->set_locale(locale);
	}
	translation_server->load_translations();
	ResourceLoader::load_translation_remaps(); 
	ResourceLoader::load_path_remaps();
	register_scene_types();
	register_driver_types();
	initialize_modules(MODULE_INITIALIZATION_LEVEL_SCENE);
	GDExtensionManager::get_singleton()->initialize_extensions(GDExtension::INITIALIZATION_LEVEL_SCENE);
#ifdef TOOLS_ENABLED
	ClassDB::set_current_api(ClassDB::API_EDITOR);
	register_editor_types();
	initialize_modules(MODULE_INITIALIZATION_LEVEL_EDITOR);
	GDExtensionManager::get_singleton()->initialize_extensions(GDExtension::INITIALIZATION_LEVEL_EDITOR);
	ClassDB::set_current_api(ClassDB::API_CORE);
#endif
	register_platform_apis();
	
	initialize_theme_db();