Extra safety on account-level DELETE

I just noticed tonight when adding a bunch of stuff to Swiftly that
the Bulk Delete middleware uses an account-level DELETE request,
albeit with a query parameter of bulk-delete. But, one typo and,
assuming the cluster supports it and you have access, whoops, you
just marked the account for deletion!

I put a bit of extra safety on the account deletion by requiring it
to have an empty query string.

Change-Id: Ib5df11193b04eff69d14185bd9d0607169131e7f