lavfi/vf_libplacebo: drop redundant case

If the input queue is EOF, then the s->status check should already have
covered it, and prevented the code from getting this far.

If we still hit this case for some reason, it's probably a bug. Better
to hit the AVERROR_BUG branch.

libavfilter/vf_libplacebo.c

@@ -949,9 +949,6 @@ static int libplacebo_activate(AVFilterContext *ctx)
             if (!s->fps.num)
                 av_fifo_drain2(s->out_pts, 1);
             return output_frame_mix(ctx, &mix, pts);
-        case PL_QUEUE_EOF:
-            ff_outlink_set_status(outlink, AVERROR_EOF, pts);
-            return 0;
         case PL_QUEUE_ERR:
             return AVERROR_EXTERNAL;
         }