lavfi: remove init and check of rate and layout.

The sample rate and channel layout are negotiated and set
by the filter graph system.

libavfilter/avfilter.c

@@ -281,17 +281,8 @@ int avfilter_config_links(AVFilterContext *filter)
 
             case AVMEDIA_TYPE_AUDIO:
                 if (inlink) {
-                    if (!link->sample_rate)
-                        link->sample_rate = inlink->sample_rate;
                     if (!link->time_base.num && !link->time_base.den)
                         link->time_base = inlink->time_base;
-                    if (!link->channel_layout)
-                        link->channel_layout = inlink->channel_layout;
-                } else if (!link->sample_rate) {
-                    av_log(link->src, AV_LOG_ERROR,
-                           "Audio source filters must set their output link's "
-                           "sample_rate\n");
-                    return AVERROR(EINVAL);
                 }
 
                 if (!link->time_base.num && !link->time_base.den)