### 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
project_manager = !found_project && !cmdline_tool;
	}
	if (project_manager) {
		Engine::get_singleton()->set_project_manager_hint(true);
	}
#endif
	GLOBAL_DEF("debug/file_logging/enable_file_logging", false);
	
	
	
	
	GLOBAL_DEF("debug/file_logging/enable_file_logging.pc", true);
	GLOBAL_DEF("debug/file_logging/log_path", "user://logs/godot.log");
	GLOBAL_DEF(PropertyInfo(Variant::INT, "debug/file_logging/max_log_files", PROPERTY_HINT_RANGE, "0,20,1,or_greater"), 5);
	if (!project_manager && !editor && FileAccess::get_create_func(FileAccess::ACCESS_USERDATA) &&
			GLOBAL_GET("debug/file_logging/enable_file_logging")) {
		
		
		String base_path = GLOBAL_GET("debug/file_logging/log_path");
		int max_files = GLOBAL_GET("debug/file_logging/max_log_files");
		OS::get_singleton()->add_logger(memnew(RotatedFileLogger(base_path, max_files)));
	}
	if (main_args.size() == 0 && String(GLOBAL_GET("application/run/main_scene")) == "") {
#ifdef TOOLS_ENABLED
		if (!editor && !project_manager) {
#endif
			const String error_msg = "Error: Can't run project: no main scene defined in the project.\n";
			OS::get_singleton()->print("%s", error_msg.utf8().get_data());
			OS::get_singleton()->alert(error_msg);