In the driver example, a sed class script is used to add an entry for the driver to the file /etc/devlink.tab. This file is used by the devlinks command to create symbolic links from /dev into /devices. This is the sed script:
# sed class script to modify /etc/devlink.tab !install /name=sst;/d $i\ type=ddi_pseudo;name=sst;minor=character rsst\\A1 !remove /name=sst;/d |
The pkgrm command does not run the removal part of the script. You may need to add a line to the preremove script to run sed directly to remove the entry from the /etc/devlink.tab file.