### 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
#ifdef TESTS_ENABLED
	for (int x = 0; x < argc; x++) {
		if ((strncmp(argv[x], "--test", 6) == 0) && (strlen(argv[x]) == 6)) {
			tests_need_run = true;
			
			
			test_setup();
			int status = test_main(argc, argv);
			test_cleanup();
			return status;
		}
	}
#endif
	tests_need_run = false;
	return 0;
}
/* Engine initialization
 *
 * Consists of several methods that are called by each platform's specific main(argc, argv).
 * To fully understand engine init, one should therefore start from the platform's main and
 * see how it calls into the Main class' methods.
 *
 * The initialization is typically done in 3 steps (with the setup2 step triggered either
 * automatically by setup, or manually in the platform's main).
 *