### 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()->print("Missing tablet driver argument, aborting.\n");
				goto error;
			}
		} else if (I->get() == "--single-window") { 
			single_window = true;
		} else if (I->get() == "-t" || I->get() == "--always-on-top") { 
			init_always_on_top = true;
		} else if (I->get() == "--resolution") { 
			if (I->next()) {
				String vm = I->next()->get();
				if (!vm.contains("x")) { 
					OS::get_singleton()->print("Invalid resolution '%s', it should be e.g. '1280x720'.\n",
							vm.utf8().get_data());
					goto error;
				}
				int w = vm.get_slice("x", 0).to_int();
				int h = vm.get_slice("x", 1).to_int();
				if (w <= 0 || h <= 0) {
					OS::get_singleton()->print("Invalid resolution '%s', width and height must be above 0.\n",
							vm.utf8().get_data());
					goto error;
				}
				window_size.width = w;
				window_size.height = h;
				force_res = true;
				N = I->next()->next();
			} else {
				OS::get_singleton()->print("Missing resolution argument, aborting.\n");
				goto error;
			}