### 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 (initial_position_type == 1) {
			if (!init_use_custom_screen) {
				init_screen = DisplayServer::SCREEN_PRIMARY;
				init_use_custom_screen = true;
			}
		} else if (initial_position_type == 2) {
			if (!init_use_custom_screen) {
				init_screen = GLOBAL_GET("display/window/size/initial_screen").operator int();
				init_use_custom_screen = true;
			}
		}
	}
	GLOBAL_DEF("internationalization/locale/include_text_server_data", false);
	OS::get_singleton()->_allow_hidpi = GLOBAL_DEF("display/window/dpi/allow_hidpi", true);
	OS::get_singleton()->_allow_layered = GLOBAL_DEF("display/window/per_pixel_transparency/allowed", false);
#ifdef TOOLS_ENABLED
	if (editor || project_manager) {
		
		OS::get_singleton()->_allow_hidpi = true;
		
		OS::get_singleton()->set_environment("DISABLE_MANGOHUD", "1"); 
		OS::get_singleton()->set_environment("DISABLE_RTSS_LAYER", "1"); 
		OS::get_singleton()->set_environment("DISABLE_VKBASALT", "1");
	} else {
		
		OS::get_singleton()->unset_environment("DISABLE_MANGOHUD");
		OS::get_singleton()->unset_environment("DISABLE_RTSS_LAYER");
		OS::get_singleton()->unset_environment("DISABLE_VKBASALT");
	}
#endif