ffmpegthumbs: fixup inputs and outputs

pkgs/applications/kde/ffmpegthumbs.nix

···
     maintainers = [ lib.maintainers.ttuegel ];
   };
   nativeBuildInputs = [ extra-cmake-modules ];
-  propagatedBuildInputs = [ ffmpeg kio ];
+  buildInputs = [ ffmpeg kio ];
 }