add_browserid: delete any matching unconfirmed emails
add_browserid: delete any matching unconfirmed emails

If an email is confirmed through Persona, we might as well clean
up any unconfirmed emails a user has for it.

libravatar/libravatar,libravatar/libravatar,libravatar/libravatar,libravatar/libravatar,libravatar/libravatar,libravatar/libravatar,libravatar/libravatar