refactor(bem): remove BemWithSpecificContext from MenuContext

Cleaned up MenuContext to remove unused Block/Elem exports.
- Removed BemWithSpecificContext import
- Removed Block/Elem exports (no longer used after Menu.jsx migration)
- Only MenuContext remains (still needed for menu state)
- No behavior change

Part of Label Studio BEM migration (Additional files)

Author: luarmr

web/apps/labelstudio/src/components/Menu/MenuContext.js

@@ -1,5 +1,3 @@
 import React from "react";
-import { BemWithSpecificContext } from "../../utils/bem";
 
 export const MenuContext = React.createContext();
-export const { Block, Elem } = BemWithSpecificContext();