[SCSI] fix media change events for polled devices

Commit:
  a341cd0f (SCSI: add asynchronous event notification API)
breaks:
  285e9670 (sr,sd: send media state change modification events)
by introducing an event filter, which is removed here, to make
events, we are depending on, happen again.

Fix this by removing the event filter.  It's pretty much broken at the
moment, since a user can't set it (the attribute being read only).  A
proper fix will be to make the event discriminator distinguish between
AN and Polled media change events.

Cc: David Zeuthen <david@fubar.dk>
Cc: kristen accardi <kaccardi@gmail.com>
Cc: Jeff Garzik <jeff@garzik.org>
Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>