stellio: drop image.repart.enable shim

nixpkgs declares the option again.

machines/stellio/configuration.nix

@@ -10,16 +10,6 @@
     inputs.matthew-hardware.nixosModules.mt7986a-glinet-gl-mt6000
   ];
 
-  # matthew-hardware's common/generic-uefi-image.nix still sets
-  # `image.repart.enable = true`; nixpkgs removed that option (importing
-  # image/repart.nix now always defines system.build.image). Declare it so the
-  # definition has somewhere to land. Drop once upstream stops setting it.
-  options.image.repart.enable = lib.mkOption {
-    type = lib.types.bool;
-    default = true;
-    internal = true;
-  };
-
   config = {
     hardware.mt7986a-glinet-gl-mt6000.enable = true;
     hardware.mt7986a-glinet-gl-mt6000.zealous = true;