nixos/wyoming/piper: remove piper package option (#446149)

nixos/modules/services/home-automation/wyoming/piper.nix

···
             options = {
               enable = mkEnableOption "Wyoming Piper server";
 
-              piper = mkPackageOption pkgs "piper-tts" { };
-
               voice = mkOption {
                 type = str;
                 example = "en-us-ryan-medium";
···
                 "/var/lib/wyoming/piper"
                 "--uri"
                 options.uri
-                "--piper"
-                (lib.getExe options.piper)
                 "--voice"
                 options.voice
                 "--speaker"