Rework the BIO_DELETE code slightly. Always queue the BIO_DELETE
requests on the trim_queue, even for the CFA ERASE. This allows us, in
the future, to collapse adjacent requests. Since CFA ERASE is only for
CF cards, and it is so restrictive in what it can do, the collapse
code is not presently here. This also brings the ada driver more in
line with the da driver's treatment of BIO_DELETEs.

Reviewed by: mav@