firefoxen: remove unused gstreamer dependencies

Firefox and, by extension, Tor browser don't support gstreamer any more, this
removes what are effectively unused dependencies.

https://bugzilla.mozilla.org/show_bug.cgi?id=1234092 "Remove gstreamer support"

pkgs/applications/networking/browsers/tor-browser-bundle-bin/default.nix

@@ -29,13 +29,10 @@
 
 # Media support (implies audio support)
 , mediaSupport ? false
-, gstreamer
-, gst-plugins-base
-, gst-plugins-good
-, gst-ffmpeg
-, gmp
 , ffmpeg
 
+, gmp
+
 # Pluggable transport dependencies
 , python27
 
@@ -85,20 +82,9 @@ let
   ]
   ++ optionals pulseaudioSupport [ libpulseaudio ]
   ++ optionals mediaSupport [
-    gstreamer
-    gst-plugins-base
-    gmp
     ffmpeg
   ];
 
-  gstPluginsPath = concatMapStringsSep ":" (x:
-    "${x}/lib/gstreamer-0.10") [
-      gstreamer
-      gst-plugins-base
-      gst-plugins-good
-      gst-ffmpeg
-    ];
-
   # Library search path for the fte transport
   fteLibPath = makeLibraryPath [ stdenv.cc.cc gmp ];
 
@@ -366,10 +352,6 @@ stdenv.mkDerivation rec {
       TOR_CONTROL_PORT="\''${TOR_CONTROL_PORT:-}" \
       TOR_SOCKS_PORT="\''${TOR_SOCKS_PORT:-}" \
       \
-      GST_PLUGIN_SYSTEM_PATH="${optionalString mediaSupport gstPluginsPath}" \
-      GST_REGISTRY="/dev/null" \
-      GST_REGISTRY_UPDATE="no" \
-      \
       FONTCONFIG_FILE="$FONTCONFIG_FILE" \
       \
       LD_LIBRARY_PATH="$libPath" \