Remove reference to sys/dev/dpt/dpt_control.c.  It was removed back in 2001 after having
never been updated for CAM changes in 1998.
Remove dpt_isa.c and commented out references to it.  It was never connected
to the build in either sys/conf/files* or sys/modules/dpt/Makefile.  Also,
it was denoted as "doesn't quite work yet" when the file was initially added
(which may account for it never having been hooked up to the build).
Drop mention of ISA cards.  Note that I have no idea what to cull from the
supported hardware list.  Judging by the PCI driver attachment, dpt_pci.c
only supports a single adapter rather than the various PCI adapters listed.
The list of EISA adapters listed somewhat overlaps with the device IDs in
dpt_eisa.c.  It's not clear which devices are ISA-only devices.