Remove Install page from Available updates report hierarchy

This page is going to be deprecated and removed once project browser exists and is stable. So I'm not sure it's worth removing it. But yes, it's the identical form, available from 3 different locations.

Per @xjm, we can proceed to remove this UI entirely. Closing this in favor of 📌 Remove adding an extension via a URL Fixed which is a more complete solution.

Thanks,
-Derek