### 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
DisplayServer::get_singleton()->set_icon(icon);
		}
#endif
	}
	DisplayServer::set_early_window_clear_color_override(false);
	MAIN_PRINT("Main: DCC");
	RenderingServer::get_singleton()->set_default_clear_color(
			GLOBAL_GET("rendering/environment/defaults/default_clear_color"));
	GLOBAL_DEF(PropertyInfo(Variant::STRING, "application/config/icon", PROPERTY_HINT_FILE, "*.png,*.webp,*.svg"), String());
	GLOBAL_DEF(PropertyInfo(Variant::STRING, "application/config/macos_native_icon", PROPERTY_HINT_FILE, "*.icns"), String());
	GLOBAL_DEF(PropertyInfo(Variant::STRING, "application/config/windows_native_icon", PROPERTY_HINT_FILE, "*.ico"), String());
	Input *id = Input::get_singleton();
	if (id) {
		agile_input_event_flushing = GLOBAL_DEF("input_devices/buffering/agile_event_flushing", false);
		if (bool(GLOBAL_DEF_BASIC("input_devices/pointing/emulate_touch_from_mouse", false)) &&
				!(editor || project_manager)) {
			if (!DisplayServer::get_singleton()->is_touchscreen_available()) {
				/
				id->set_emulate_touch_from_mouse(true);
			}
		}
		id->set_emulate_mouse_from_touch(bool(GLOBAL_DEF_BASIC("input_devices/pointing/emulate_mouse_from_touch", true)));
	}
	MAIN_PRINT("Main: Load Translations and Remaps");
	translation_server->setup(); 
	if (!locale.is_empty()) {
		translation_server->set_locale(locale);
	}
	translation_server->load_translations();
	ResourceLoader::load_translation_remaps();