scripts-remove works poorly with non-Athena accounts

[adehnert]

It's unclear that we should care, but scripts-remove handles being given the "Your personal Athena account" option when run from a non-Athena account (say, debathena-standard) fairly poorly. It seems reasonable for a user to expect that option to do something reasonable with $ATHENA_USER, but currently it doesn't respect $ATHENA_USER at all, and attempts to use $HOME instead of the $ATHENA_USER's corresponding Athena locker.

In sufficiently contrived situations (e.g., $USER corresponds to an Athena user with the same sql.mit.edu password as you), I think this might be able to cause data loss. That said, I haven't been able to think of any situations that actually strike me as particularly likely.