### 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
sml->get_root()->set_default_canvas_item_texture_repeat(
					Viewport::DefaultCanvasItemTextureRepeat(texture_repeat));
		}
#ifdef TOOLS_ENABLED
		if (editor) {
			bool editor_embed_subwindows = EditorSettings::get_singleton()->get_setting(
					"interface/editor/single_window_mode");
			if (editor_embed_subwindows) {
				sml->get_root()->set_embedding_subwindows(true);
			}
		}
#endif
		String local_game_path;
		if (!game_path.is_empty() && !project_manager) {
			local_game_path = game_path.replace("\\", "/");
			if (!local_game_path.begins_with("res://")) {
				bool absolute =
						(local_game_path.size() > 1) && (local_game_path[0] == '/' || local_game_path[1] == ':');
				if (!absolute) {
					if (ProjectSettings::get_singleton()->is_using_datapack()) {
						local_game_path = "res://" + local_game_path;
					} else {
						int sep = local_game_path.rfind("/");
						if (sep == -1) {
							Ref<DirAccess> da = DirAccess::create(DirAccess::ACCESS_FILESYSTEM);
							local_game_path = da->get_current_dir().path_join(local_game_path);
						} else {
							Ref<DirAccess> da = DirAccess::open(local_game_path.substr(0, sep));
							if (da.is_valid()) {
								local_game_path = da->get_current_dir().path_join(