### 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
found = true;
					break;
				}
			}
		}
		if (!found) {
			OS::get_singleton()->print("Unknown rendering driver '%s', aborting.\nValid options are ",
					rendering_driver.utf8().get_data());
			for (int i = 0; i < DisplayServer::get_create_function_count(); i++) {
				Vector<String> r_drivers = DisplayServer::get_create_function_rendering_drivers(i);
				for (int d = 0; d < r_drivers.size(); d++) {
					OS::get_singleton()->print("'%s', ", r_drivers[d].utf8().get_data());
				}
			}
			OS::get_singleton()->print(".\n");
			goto error;
		}
		
		if (rendering_method.is_empty()) {
			if (rendering_driver == "opengl3") {
				rendering_method = "gl_compatibility";
			} else {
				rendering_method = "forward_plus";
			}
		}
		
		bool valid_combination = false;
		Vector<String> available_drivers;
#ifdef VULKAN_ENABLED
		if (rendering_method == "forward_plus" || rendering_method == "mobile") {