gst-plugins-bad: remove libvdpau dependency

vdpau is a mostly-unsupported hardware acceleration library.
Support for vdpau integration was removed upstream
in 4ff14c0e746eb26874a696b3b71543387fbefa3b [1],
which took effect in 1.17.1 released June 2020 [2].

[1] https://github.com/GStreamer/gst-plugins-bad/commit/4ff14c0e746eb26874a696b3b71543387fbefa3b
[2] https://github.com/GStreamer/gst-plugins-bad/releases/tag/1.17.1

pkgs/development/libraries/gstreamer/bad/default.nix

@@ -78,7 +78,6 @@
 , svt-av1
 , fluidsynth
 , libva
-, libvdpau
 , wayland
 , libwebp
 , xvidcore
@@ -196,7 +195,6 @@ stdenv.mkDerivation (finalAttrs: {
     soundtouch
     srtp
     fluidsynth
-    libvdpau
     libwebp
     xvidcore
     gnutls