### 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
rendering_server->set_print_gpu_profile(true);
	}
	if (Engine::get_singleton()->get_write_movie_path() != String()) {
		movie_writer = MovieWriter::find_writer_for_file(Engine::get_singleton()->get_write_movie_path());
		if (movie_writer == nullptr) {
			ERR_PRINT("Can't find movie writer for file type, aborting: " + Engine::get_singleton()->get_write_movie_path());
			Engine::get_singleton()->set_write_movie_path(String());
		}
	}
#ifdef UNIX_ENABLED
	
	if (OS::get_singleton()->get_environment("USER") == "root" && !OS::get_singleton()->has_environment("GODOT_SILENCE_ROOT_WARNING")) {
		WARN_PRINT("Started the engine as `root`/superuser. This is a security risk, and subsystems like audio may not work correctly.\nSet the environment variable `GODOT_SILENCE_ROOT_WARNING` to 1 to silence this warning.");
	}
#endif
	OS::get_singleton()->initialize_joypads();
	
	AudioDriverManager::initialize(audio_driver_idx);
	print_line(" "); 
	
	audio_server = memnew(AudioServer);
	audio_server->init();
	
	xr_server = memnew(XRServer);
	register_core_singletons();
	MAIN_PRINT("Main: Setup Logo");
#if !defined(TOOLS_ENABLED) && (defined(WEB_ENABLED) || defined(ANDROID_ENABLED))
	bool show_logo = false;
#else
	bool show_logo = true;