Merge branch 'remove-obsolete-nixpkgs-file' into 'develop'

Remove obsolete nixpkgs pin

See merge request !356

nixpkgs-2105.nix

-# This actually imports nixos-21.11 but we need to keep this file around so that
-# upgrades work, as the on-node deployment script expects this file in the checkout.
-# See https://whetstone.private.storage/privatestorage/PrivateStorageio/-/merge_requests/222#note_18600
-# This file can be removed once all nodes have been updated to point to the new file.
-
-import ./nixpkgs.nix