### 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
}
				}
				/
				List<Node *> to_add;
				for (const KeyValue<StringName, ProjectSettings::AutoloadInfo> &E : autoloads) {
					const ProjectSettings::AutoloadInfo &info = E.value;
					Node *n = nullptr;
					if (ResourceLoader::get_resource_type(info.path) == "PackedScene") {
						/
						Ref<PackedScene> scn;
						scn.instantiate();
						scn->set_path(info.path);
						scn->reload_from_file();
						ERR_CONTINUE_MSG(!scn.is_valid(), vformat("Can't autoload: %s.", info.path));
						if (scn.is_valid()) {
							n = scn->instantiate();
						}
					} else {
						Ref<Resource> res = ResourceLoader::load(info.path);
						ERR_CONTINUE_MSG(res.is_null(), vformat("Can't autoload: %s.", info.path));
						Ref<Script> script_res = res;
						if (script_res.is_valid()) {
							StringName ibt = script_res->get_instance_base_type();
							bool valid_type = ClassDB::is_parent_class(ibt, "Node");
							ERR_CONTINUE_MSG(!valid_type, vformat("Script does not inherit from Node: %s.", info.path));
							Object *obj = ClassDB::instantiate(ibt);
							ERR_CONTINUE_MSG(!obj, vformat("Cannot instance script for autoload, expected 'Node' inheritance, got: %s."));
							n = Object::cast_to<Node>(obj);
							n->set_script(script_res);
						}