config: AFS_SHORTGID no longer in use

Remove the AFS_SHORTGID macro from the param header files.  There
are no usages in the rest of the source tree.

Change-Id: I417b6e90fa9a094bfef727134b640964596eceb3
Reviewed-on: http://gerrit.openafs.org/11345
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Garrett Wollman <wollman@csail.mit.edu>
Reviewed-by: D Brashear <shadow@your-file-system.com>