### 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
if (rtm == -1) {
		rtm = GLOBAL_DEF("rendering/driver/threads/thread_model", OS::RENDER_THREAD_SAFE);
	}
	if (rtm >= 0 && rtm < 3) {
		if (editor) {
			rtm = OS::RENDER_THREAD_SAFE;
		}
		OS::get_singleton()->_render_thread_mode = OS::RenderThreadMode(rtm);
	}
	
	
	
	DEV_ASSERT(NULL_DISPLAY_DRIVER == DisplayServer::get_create_function_name(DisplayServer::get_create_function_count() - 1));
	for (int i = 0; i < DisplayServer::get_create_function_count(); i++) {
		String name = DisplayServer::get_create_function_name(i);
		if (display_driver == name) {
			display_driver_idx = i;
			break;
		}
	}
	if (display_driver_idx < 0) {
		
		
		display_driver_idx = 0;
	}
	
	
	OS::get_singleton()->set_display_driver_id(display_driver_idx);
	GLOBAL_DEF_RST_NOVAL("audio/driver/driver", AudioDriverManager::get_driver(0)->get_name());
	if (audio_driver.is_empty()) {