ptserver: Check for -restricted in SPR_Delete

ptserver: Check for -restricted in SPR_Delete

Currently, all prdb write operations, except for SPR_Delete, will fail
with PRPERM if called by a non-system:administrators caller while
restricted mode is active.  SPR_Delete is missing this check, and so
is not affected by the -restricted option.

Fix this by inserting the same check for -restricted as all other code
paths that check for -restricted.

Change-Id: I35f19d0b715423cd91769e6de845efa330368e50
Reviewed-on: https://gerrit.openafs.org/13374
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>