vdpau: drop required/deprecated access to a libavcodec struct field

Before the bitstream_buffers field was deprecated, you had to free it,
otherwise you would leak memory.

(Although vdpau.c uses a new API, they managed to introduce a new
deprecation this quickly. This is a complaint.)

This introduces a memory leak of 12 bytes per file on every file on some
_older_ libavcodec versions. This is minor enough that I don't care.

video/decode/vdpau.c

@@ -194,9 +194,6 @@ static void uninit(struct lavc_ctx *ctx)
     if (p->context.decoder != VDP_INVALID_HANDLE)
         p->vdp->decoder_destroy(p->context.decoder);
 
-    // Free bitstream buffers allocated by libavcodec
-    av_freep(&p->context.bitstream_buffers);
-
     talloc_free(p);
 
     ctx->hwdec_priv = NULL;