### 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
OS::get_singleton()->finalize();
	if (translation_server) {
		memdelete(translation_server);
	}
	if (tsman) {
		memdelete(tsman);
	}
	if (physics_server_3d_manager) {
		memdelete(physics_server_3d_manager);
	}
	if (physics_server_2d_manager) {
		memdelete(physics_server_2d_manager);
	}
	if (globals) {
		memdelete(globals);
	}
	if (packed_data) {
		memdelete(packed_data);
	}
	if (engine) {
		memdelete(engine);
	}
	unregister_core_driver_types();
	uninitialize_modules(MODULE_INITIALIZATION_LEVEL_CORE);
	unregister_core_extensions();
	unregister_core_types();
	OS::get_singleton()->finalize_core();
}
#endif
int Main::test_entrypoint(int argc, char *argv[], bool &tests_need_run) {