Remove unused cam ccb flags

These flags have been unused for some time. Some of them were in the
CAM2 specification, but CAM has moved on a bit from that. Some were
used in the old Pluto VideoSpace (and AirSpace) systems which had the
video playback I/O scheduler in userspace, but have been unused since
then.

Reviewed by: chuck, ken
Differential Revision: https://reviews.freebsd.org/D24008