remove hydra as binary cache

roles/common.nix

@@ -17,13 +17,9 @@
   # Nix
   nixpkgs.config.allowUnfree = true;
 
-  nix.binaryCaches = [
-    https://hydra.nixos.org
-  ];
 
   nix.trustedBinaryCaches = config.nix.binaryCaches ++ [http://hydra.cryp.to];
   nix.binaryCachePublicKeys = [
-    "hydra.nixos.org-1:CNHJZBh9K4tP3EKF6FkkgeVYsS3ohTl+oS0Qa8bezVs="
     "hydra.cryp.to-1:8g6Hxvnp/O//5Q1bjjMTd5RO8ztTsG8DKPOAg9ANr2g="
   ];