Should we restore the registration record removing step in Clear Registration?

[jungkees]

In #614 (comment), @asakusuma pointed:

should Clear Registration call Remove scope to registration map as well? unregister() is not the only entry point into Clear Registration.

I missed that while reviewing #1415. I think we should restore the registration record removing step in Clear Registration algorithm.

Perhaps we can even use the uninstalling flag as we used to while keeping "killing the resurrection" part in Register algorithm as @jakearchibald did in the PR? I.e., for the unregistered record, subsequent navigations won't match it based on the flag, and subsequent Register will just replace the record.

[jakearchibald]

Thanks for catching this. PR: #1434