avfilter/af_amerge: Remove always-false samplerate check

This filter uses ff_set_common_all_samplerates().
Also don't overwrite outlink->sample_rate in config_output;
it is harmless, because it is overwritten with the value it already
had, but it is an API violation.
Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavfilter/af_amerge.c

@@ -151,17 +151,7 @@ static int config_output(AVFilterLink *outlink)
     AVBPrint bp;
     int i;
 
-    for (i = 1; i < s->nb_inputs; i++) {
-        if (ctx->inputs[i]->sample_rate != ctx->inputs[0]->sample_rate) {
-            av_log(ctx, AV_LOG_ERROR,
-                   "Inputs must have the same sample rate "
-                   "%d for in%d vs %d\n",
-                   ctx->inputs[i]->sample_rate, i, ctx->inputs[0]->sample_rate);
-            return AVERROR(EINVAL);
-        }
-    }
     s->bps = av_get_bytes_per_sample(ctx->outputs[0]->format);
-    outlink->sample_rate = ctx->inputs[0]->sample_rate;
     outlink->time_base   = ctx->inputs[0]->time_base;
 
     av_bprint_init(&bp, 0, AV_BPRINT_SIZE_AUTOMATIC);