Delete some unreferenced SMD, ST506 and archaic SCSI #define's

Delete some unreferenced SMD, ST506 and archaic SCSI #define's
that use d_drivedata.

Since nothing else in the tree refers to d_drivedata other than
/etc/disktab parsing and no /etc/disktab entry utilizes the
:d[0-4]: attributes, stop disklabel(8) both printing "drivedata:
0" and paying attention to any "drivedata: ..." lines in ascii
labels being read.

ok jsg@ miod@