Crash in systemd service "nvidia-persistenced" because of deletion of "nvidia-persistenced" user profile on old package "nvidia-compute-utils" purge

[fprietog]

Problem summary:
----------------
Every time I upgraded nvidia drivers from version XXX to YYY there is a crash in systemd service "nvidia-persistenced" because of deletion of "nvidia-persistenced" user profile after old package "nvidia-compute-utils-XXX" is purged.

Example of the problem:
-----------------------
- Current driver installed: "nvidia-driver-535"
- Upgrade to "nvidia-driver-545"
- The upgrade will remove previous "nvidia-driver-535" related packages but some of them are not purged. One of these non purged packages is "nvidia-compute-utils-535".
- After "nvidia-driver-545" was installed there is a warning on every apt upgrade because it detects packages uninstalled with remaining configuration files, "nvidia-compute-utils-535" package among them, and if you purge that package (something you should do sooner or later) the user profile "nvidia-persistenced" is deleted and systemd service "nvidia-persistenced" will crash in next boot until that profile is created again.

The problem is caused because of this automation in "nvidia-compute-utils" .deb package:
- On install, "postinst" script creates the user and group for "nvidia-persistenced".
- On remove or purge, "postrm" script deletes the "nvidia-persistenced" user.

So, when upgraded driver from 535 to 545:
- Package "nvidia-compute-utils-535" is removed but not purged. (user "nvidia-persistenced" is deleted, OK)
- Package "nvidia-compute-utils-545" is installed. (user "nvidia-persistenced" is created, OK)
- When old "nvidia-compute-utils-535" package is purged it deletes "nvidia-persistenced" user profile despite the fact that a newer version of the package is installed and that user is needed.

Possible solution:
------------------
Remove deletion of that user profile in "nvidia-compute-utils" package "postrm" file when "purge" is executed, leaving it only for "remove" in this sentence:
...
case "$1" in
    remove|purge)
        # Remove the nvidia-persistenced user
...