Revert "nixops: enable fish-nix-shell on rpi"

Still fails with 'exec format error'.

This reverts commit 3e19ee59c9.

nixops/rpi.nix

@@ -53,12 +53,8 @@ in
   documentation.enable = false;
   environment.systemPackages = with pkgs; [
     psmisc wget vim git usbutils lm_sensors file telnet mosh tmux xc3sprog m-labs.openocd screen gdb minicom picocom
-    (import ./fish-nix-shell)
   ];
   programs.fish.enable = true;
-  programs.fish.promptInit = ''
-    fish-nix-shell --info-right | source
-  '';
   programs.wireshark.enable = true;
 
   nix.binaryCachePublicKeys = ["nixbld.m-labs.hk-1:5aSRVA5b320xbNvu30tqxVPXpld73bhtOeH6uAjRyHc="];