fix(uconsole): stop following nixpkgs for nixos-uconsole and nixos-raspberrypi

Remove inputs.nixpkgs.follows so these inputs use their own pinned nixpkgs.
This lets the uConsole build use the nixos-uconsole Cachix cache for the kernel,
avoiding 4h kernel recompilation on every config change.

flake.nix

@@ -18,11 +18,9 @@
     };
     nixos-uconsole = {
       url = "github:nixos-uconsole/nixos-uconsole";
-      inputs.nixpkgs.follows = "nixpkgs";
     };
     nixos-raspberrypi = {
       url = "github:nvmd/nixos-raspberrypi/v1.20260517.0";
-      inputs.nixpkgs.follows = "nixpkgs";
     };
     self.submodules = true;
   };