### 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
available_drivers.push_back("vulkan");
		}
#endif
#ifdef GLES3_ENABLED
		if (rendering_method == "gl_compatibility") {
			available_drivers.push_back("opengl3");
		}
#endif
		if (available_drivers.is_empty()) {
			OS::get_singleton()->print("Unknown renderer name '%s', aborting.\n", rendering_method.utf8().get_data());
			goto error;
		}
		for (int i = 0; i < available_drivers.size(); i++) {
			if (rendering_driver == available_drivers[i]) {
				valid_combination = true;
				break;
			}
		}
		if (!valid_combination) {
			OS::get_singleton()->print("Invalid renderer/driver combination '%s' and '%s', aborting. %s only supports the following drivers ", rendering_method.utf8().get_data(), rendering_driver.utf8().get_data(), rendering_method.utf8().get_data());
			for (int d = 0; d < available_drivers.size(); d++) {
				OS::get_singleton()->print("'%s', ", available_drivers[d].utf8().get_data());
			}
			OS::get_singleton()->print(".\n");
			goto error;
		}
	}
	default_renderer = renderer_hints.get_slice(",", 0);
	GLOBAL_DEF_RST_BASIC(PropertyInfo(Variant::STRING, "rendering/renderer/rendering_method", PROPERTY_HINT_ENUM, renderer_hints), default_renderer);
	GLOBAL_DEF_RST_BASIC("rendering/renderer/rendering_method.mobile", default_renderer_mobile);