chore(ops/git-serving): Remove josh state from whitby backups

As cschilling explained on cl/3563, there isn't actually anything in
this state that we *need* to persist. We're still keeping it in a
persistent directory on disk as this serves as an optimisation after
restarts of josh.

Change-Id: Ia88886792a5acac34508b5b8a669bd519ca033de
Reviewed-on: https://cl.tvl.fyi/c/depot/+/3631
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>

ops/modules/git-serving.nix

@@ -49,7 +49,5 @@ in {
         ExecStart = "${depot.third_party.josh}/bin/josh-proxy --no-background --local /var/lib/josh --port ${toString cfg.joshPort} --remote https://cl.tvl.fyi/";
       };
     };
-
-    services.depot.restic.paths = [ "/var/lib/josh" ];
   };
 }