literalExample is deprecated and overused. See:
https://whetstone.privatestorage.io/privatestorage/PrivateStorageio/-/merge_requests/201#note_16966

This is what we wanted and much more directly.  It also avoids the gradual
lengthening of the path by always setting the path to nixpkgs-2105 instead of
some derivative of whatever the path was last time.

The old version of nixpkgs let us get away with setting neither isNormalUser
nor isSystemUser but setting all of the things a normal user would get
directly.  The new version of nixpkgs demands one of these flags be set.  So,
set it, and remove all of the redundant settings that it implies.

Also add my key to local secrets for the moment because otherwise localdev
grid cannot build itself :/