### 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
}
	
	OS::get_singleton()->ensure_user_data_dir();
	initialize_modules(MODULE_INITIALIZATION_LEVEL_CORE);
	register_core_extensions(); 
	ResourceUID::get_singleton()->load_from_cache(); 
	if (ProjectSettings::get_singleton()->has_custom_feature("dedicated_server")) {
		audio_driver = NULL_AUDIO_DRIVER;
		display_driver = NULL_DISPLAY_DRIVER;
	}
	GLOBAL_DEF(PropertyInfo(Variant::INT, "network/limits/debugger/max_chars_per_second", PROPERTY_HINT_RANGE, "0, 4096, 1, or_greater"), 32768);
	GLOBAL_DEF(PropertyInfo(Variant::INT, "network/limits/debugger/max_queued_messages", PROPERTY_HINT_RANGE, "0, 8192, 1, or_greater"), 2048);
	GLOBAL_DEF(PropertyInfo(Variant::INT, "network/limits/debugger/max_errors_per_second", PROPERTY_HINT_RANGE, "0, 200, 1, or_greater"), 400);
	GLOBAL_DEF(PropertyInfo(Variant::INT, "network/limits/debugger/max_warnings_per_second", PROPERTY_HINT_RANGE, "0, 200, 1, or_greater"), 400);
	EngineDebugger::initialize(debug_uri, skip_breakpoints, breakpoints, []() {
		if (editor_pid) {
			DisplayServer::get_singleton()->enable_for_stealing_focus(editor_pid);
		}
	});
#ifdef TOOLS_ENABLED
	if (editor) {
		packed_data->set_disabled(true);
		Engine::get_singleton()->set_editor_hint(true);
		main_args.push_back("--editor");
		if (!init_windowed) {
			init_maximized = true;
			window_mode = DisplayServer::WINDOW_MODE_MAXIMIZED;
		}
	}
	if (!project_manager && !editor) {