### 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
if (!game_path.is_empty()) {
				Node *scene = nullptr;
				Ref<PackedScene> scenedata = ResourceLoader::load(local_game_path);
				if (scenedata.is_valid()) {
					scene = scenedata->instantiate();
				}
				ERR_FAIL_COND_V_MSG(!scene, false, "Failed loading scene: " + local_game_path);
				sml->add_current_scene(scene);
#ifdef MACOS_ENABLED
				String mac_iconpath = GLOBAL_GET("application/config/macos_native_icon");
				if (!mac_iconpath.is_empty()) {
					DisplayServer::get_singleton()->set_native_icon(mac_iconpath);
					hasicon = true;
				}
#endif
#ifdef WINDOWS_ENABLED
				String win_iconpath = GLOBAL_GET("application/config/windows_native_icon");
				if (!win_iconpath.is_empty()) {
					DisplayServer::get_singleton()->set_native_icon(win_iconpath);
					hasicon = true;
				}
#endif
				String iconpath = GLOBAL_GET("application/config/icon");
				if ((!iconpath.is_empty()) && (!hasicon)) {
					Ref<Image> icon;
					icon.instantiate();
					if (ImageLoader::load_image(iconpath, icon) == OK) {
						DisplayServer::get_singleton()->set_icon(icon);
						hasicon = true;
					}