mumble: disable grpc, pin old protobuf version

pkgs/applications/networking/mumble/default.nix

···
 , flac
 , libogg
 , libvorbis
-, grpcSupport ? false, grpc, which
 , iceSupport ? true, zeroc-ice
 , jackSupport ? false, libjack2
 , pipewireSupport ? true, pipewire
···
         "-D Ice_HOME=${lib.getDev zeroc-ice};${lib.getLib zeroc-ice}"
         "-D CMAKE_PREFIX_PATH=${lib.getDev zeroc-ice};${lib.getLib zeroc-ice}"
         "-D Ice_SLICE_DIR=${lib.getDev zeroc-ice}/share/ice/slice"
-      ]
-      ++ lib.optional grpcSupport "-D grpc=ON";
+      ];
 
     buildInputs = [ libcap ]
-      ++ lib.optional iceSupport zeroc-ice
-      ++ lib.optionals grpcSupport [ grpc which ];
+      ++ lib.optional iceSupport zeroc-ice;
   } source;
 
   source = rec {

pkgs/top-level/all-packages.nix

···
       avahi = avahi-compat;
       pulseSupport = config.pulseaudio or false;
       iceSupport = config.murmur.iceSupport or true;
-      grpcSupport = config.murmur.grpcSupport or true;
+      protobuf = protobuf3_21;
     }).murmur;
 
   mumble = (callPackages ../applications/networking/mumble {
       avahi = avahi-compat;
       jackSupport = config.mumble.jackSupport or false;
       speechdSupport = config.mumble.speechdSupport or false;
+      protobuf = protobuf3_21;
     }).mumble;
 
   mumble_overlay = callPackage ../applications/networking/mumble/overlay.nix {