gst-plugins-base: mark as broken

This will disable many reverse dependencies. If you need your program to work
you will need to migrate it to the newer gstreamer package.
https://github.com/NixOS/nixpkgs/issues/39975

pkgs/development/libraries/gstreamer/legacy/gst-plugins-base/default.nix

@@ -56,5 +56,7 @@ stdenv.mkDerivation rec {
     license     = licenses.lgpl2Plus;
     maintainers = with maintainers; [ lovek323 ];
     platforms   = platforms.unix;
+    # https://github.com/NixOS/nixpkgs/pull/91090#issuecomment-653753497
+    broken = true;
   };
 }