fix: disable channels (#161)

On machines that have channels enabled but do not have them
properly initialized (such as the recent tuffy machine, but I've
had the same problem on my laptop elmira before), running any nix
command throws up a lot of warnings.

Since I prefer using new-style nix commands with the local flake
registry (as configured in this same file), I can disable channels
across the system. This will resolve this warning with no adverse
effects.

hosts/common/core/nix.nix

@@ -47,6 +47,11 @@
         flake = inputs.nixpkgs;
       };
     };
+
+    # Since we are using flakes for most everything,
+    # remove channels to prevent heaps of warnings
+    # on systems without initialized channels
+    channel.enable = false;
   };
 
   nixpkgs = {