### 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
}
			}
			Engine::get_singleton()->startup_benchmark_end_measure(); /
		}
#ifdef TOOLS_ENABLED
		if (project_manager) {
			Engine::get_singleton()->startup_benchmark_begin_measure("project_manager");
			Engine::get_singleton()->set_editor_hint(true);
			ProjectManager *pmanager = memnew(ProjectManager);
			ProgressDialog *progress_dialog = memnew(ProgressDialog);
			pmanager->add_child(progress_dialog);
			sml->get_root()->add_child(pmanager);
			DisplayServer::get_singleton()->set_context(DisplayServer::CONTEXT_PROJECTMAN);
			Engine::get_singleton()->startup_benchmark_end_measure();
		}
		if (project_manager || editor) {
			/
			Crypto::load_default_certificates(
					EditorSettings::get_singleton()->get_setting("network/tls/editor_tls_certificates").operator String());
		}
#endif
	}
	if (!hasicon && OS::get_singleton()->get_bundle_icon_path().is_empty()) {
		Ref<Image> icon = memnew(Image(app_icon_png));
		DisplayServer::get_singleton()->set_icon(icon);
	}
	OS::get_singleton()->set_main_loop(main_loop);
	if (movie_writer) {
		movie_writer->begin(DisplayServer::get_singleton()->window_get_size(), fixed_fps, Engine::get_singleton()->get_write_movie_path());
	}