### 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
local_game_path.substr(sep + 1, local_game_path.length()));
							}
						}
					}
				}
			}
			local_game_path = ProjectSettings::get_singleton()->localize_path(local_game_path);
#ifdef TOOLS_ENABLED
			if (editor) {
				if (game_path != String(GLOBAL_GET("application/run/main_scene")) || !editor_node->has_scenes_in_session()) {
					Error serr = editor_node->load_scene(local_game_path);
					if (serr != OK) {
						ERR_PRINT("Failed to load scene");
					}
				}
				DisplayServer::get_singleton()->set_context(DisplayServer::CONTEXT_EDITOR);
				if (!debug_server_uri.is_empty()) {
					EditorDebuggerNode::get_singleton()->start(debug_server_uri);
					EditorDebuggerNode::get_singleton()->set_keep_open(true);
				}
			}
#endif
			if (!editor) {
				DisplayServer::get_singleton()->set_context(DisplayServer::CONTEXT_ENGINE);
			}
		}
		if (!project_manager && !editor) { /
			Engine::get_singleton()->startup_benchmark_begin_measure("game_load");
			/
			Crypto::load_default_certificates(GLOBAL_GET("network/tls/certificate_bundle_override"));