### 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()->add_frame_delay(DisplayServer::get_singleton()->window_can_draw());
#ifdef TOOLS_ENABLED
	if (auto_build_solutions) {
		auto_build_solutions = false;
		/
		if (!editor) {
			OS::get_singleton()->set_exit_code(EXIT_FAILURE);
			ERR_FAIL_V_MSG(true,
					"Command line option --build-solutions was passed, but no project is being edited. Aborting.");
		}
		if (!EditorNode::get_singleton()->call_build()) {
			OS::get_singleton()->set_exit_code(EXIT_FAILURE);
			ERR_FAIL_V_MSG(true,
					"Command line option --build-solutions was passed, but the build callback failed. Aborting.");
		}
	}
#endif
	return exit || auto_quit;
}
void Main::force_redraw() {
	force_redraw_requested = true;
}
/* Engine deinitialization
 *
 * Responsible for freeing all the memory allocated by previous setup steps,
 * so that the engine closes cleanly without leaking memory or crashing.
 * The order matters as some of those steps are linked with each other.
 */
void Main::cleanup(bool p_force) {