avfilter: Deduplicate default audio inputs/outputs

Lots of audio filters use very simple inputs or outputs:
An array with a single AVFilterPad whose name is "default"
and whose type is AVMEDIA_TYPE_AUDIO; everything else is unset.

Given that we never use pointer equality for inputs or outputs*,
we can simply use a single AVFilterPad instead of dozens; this
even saves .data.rel.ro (4784B here) as well as relocations.

*: In fact, several filters (like the filters in af_biquads.c)
already use the same inputs; furthermore, ff_filter_alloc()
duplicates the input and output pads so that we do not even
work with the pads directly.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavfilter/af_adynamicequalizer.c

@@ -204,13 +204,6 @@ static const AVFilterPad inputs[] = {
     },
 };
 
-static const AVFilterPad outputs[] = {
-    {
-        .name = "default",
-        .type = AVMEDIA_TYPE_AUDIO,
-    },
-};
-
 const AVFilter ff_af_adynamicequalizer = {
     .name            = "adynamicequalizer",
     .description     = NULL_IF_CONFIG_SMALL("Apply Dynamic Equalization of input audio."),
@@ -218,7 +211,7 @@ const AVFilter ff_af_adynamicequalizer = {
     .priv_class      = &adynamicequalizer_class,
     .uninit          = uninit,
     FILTER_INPUTS(inputs),
-    FILTER_OUTPUTS(outputs),
+    FILTER_OUTPUTS(ff_audio_default_filterpad),
     FILTER_QUERY_FUNC(query_formats),
     .flags           = AVFILTER_FLAG_SUPPORT_TIMELINE_INTERNAL |
                        AVFILTER_FLAG_SLICE_THREADS,