71 exercise: Typescript now supports autocomplete of defaulted generic extending ElementType

<img width="881" alt="image" src="https://github.com/total-typescript/react-typescript-tutorial/assets/115280526/8acb5f12-c5f9-4894-bb22-f8d6bde3bd58">

Therefore, `71-as-prop-with-default.solution.2.tsx` can be deleted.