mumble: Remove superfluous bundled-celt option

This option has been removed by upstream for a long time, as nobody uses
that codec anymore.

For details see upstream 4d05018c2e4f1bda48f6244b38f1e7bdc06de808

Author: dwt

pkgs/applications/networking/mumble/default.nix

@@ -116,7 +116,6 @@ let
 
       cmakeFlags = [
         "-D server=OFF"
-        "-D bundled-celt=ON"
         "-D bundled-speex=OFF"
         "-D bundle-qt-translations=OFF"
         "-D update=OFF"