### 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
}
			} else if (print_fps || GLOBAL_GET("debug/settings/stdout/print_fps")) {
				print_line(vformat("Project FPS: %d (%s mspf)", frames, rtos(1000.0 / frames).pad_decimals(2)));
			}
		} else {
			hide_print_fps_attempts--;
		}
		Engine::get_singleton()->_fps = frames;
		performance->set_process_time(USEC_TO_SEC(process_max));
		performance->set_physics_process_time(USEC_TO_SEC(physics_process_max));
		performance->set_navigation_process_time(USEC_TO_SEC(navigation_process_max));
		process_max = 0;
		physics_process_max = 0;
		navigation_process_max = 0;
		frame %= 1000000;
		frames = 0;
	}
	iterating--;
	/
	if (Input::get_singleton()->is_using_input_buffering() && !agile_input_event_flushing) {
		Input::get_singleton()->flush_buffered_events();
	}
	if (movie_writer) {
		RID main_vp_rid = RenderingServer::get_singleton()->viewport_find_from_screen_attachment(DisplayServer::MAIN_WINDOW_ID);
		RID main_vp_texture = RenderingServer::get_singleton()->viewport_get_texture(main_vp_rid);
		Ref<Image> vp_tex = RenderingServer::get_singleton()->texture_2d_get(main_vp_texture);
		movie_writer->add_frame(vp_tex);
	}
	if (fixed_fps != -1) {
		return exit;