remote build: provide a way to clean up all of a user's remote builds

### What needs to get done

This could be done with a `clean-remote-builds` command that deletes all stopped remote builds in the user's remote-build project that starts with the app's name

### Why it needs to get done

If remote build crashes, the user has to clean up manually.

Start by locating the command entry point for the proposed `clean-remote-builds` command and the code that lists stopped builds in the app-named remote-build project. Confirm cleanup is limited to stopped builds whose project starts with the app name; done means the command removes those builds while leaving other remote builds intact.

Written by the indexing model from the issue text.