### 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
ResourceLoader::load_path_remaps();
	MAIN_PRINT("Main: Load TextServer");
	/
	GLOBAL_DEF_RST("internationalization/rendering/text_driver", "");
	String text_driver_options;
	for (int i = 0; i < TextServerManager::get_singleton()->get_interface_count(); i++) {
		const String driver_name = TextServerManager::get_singleton()->get_interface(i)->get_name();
		if (driver_name == "Dummy") {
			/
			continue;
		}
		if (!text_driver_options.is_empty() && text_driver_options.find(",") == -1) {
			/
			text_driver_options += ",";
		}
		text_driver_options += driver_name;
	}
	ProjectSettings::get_singleton()->set_custom_property_info(PropertyInfo(Variant::STRING, "internationalization/rendering/text_driver", PROPERTY_HINT_ENUM, text_driver_options));
	/
	if (text_driver.is_empty()) {
		text_driver = GLOBAL_GET("internationalization/rendering/text_driver");
	}
	if (!text_driver.is_empty()) {
		/
		for (int i = 0; i < TextServerManager::get_singleton()->get_interface_count(); i++) {
			if (TextServerManager::get_singleton()->get_interface(i)->get_name() == text_driver) {
				text_driver_idx = i;
				break;
			}
		}