### 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 (I->get() == "--screen") { 
			if (I->next()) {
				init_screen = I->next()->get().to_int();
				init_use_custom_screen = true;
				N = I->next()->next();
			} else {
				OS::get_singleton()->print("Missing screen argument, aborting.\n");
				goto error;
			}
		} else if (I->get() == "--position") { 
			if (I->next()) {
				String vm = I->next()->get();
				if (!vm.contains(",")) { 
					OS::get_singleton()->print("Invalid position '%s', it should be e.g. '80,128'.\n",
							vm.utf8().get_data());
					goto error;
				}
				int x = vm.get_slice(",", 0).to_int();
				int y = vm.get_slice(",", 1).to_int();
				init_custom_pos = Point2(x, y);
				init_use_custom_pos = true;
				N = I->next()->next();
			} else {
				OS::get_singleton()->print("Missing position argument, aborting.\n");
				goto error;
			}
		} else if (I->get() == "--headless") { 
			audio_driver = NULL_AUDIO_DRIVER;
			display_driver = NULL_DISPLAY_DRIVER;
		} else if (I->get() == "--profiling") {