lavfi: remove avfilter_default_config_input_link() declaration

The function is not implemented (and possibly useless).

libavfilter/avfilter.h

@@ -447,9 +447,6 @@ void avfilter_default_filter_samples(AVFilterLink *link, AVFilterBufferRef *samp
 /** default handler for config_props() for audio/video outputs */
 int avfilter_default_config_output_link(AVFilterLink *link);
 
-/** default handler for config_props() for audio/video inputs */
-int avfilter_default_config_input_link (AVFilterLink *link);
-
 /** default handler for get_video_buffer() for video inputs */
 AVFilterBufferRef *avfilter_default_get_video_buffer(AVFilterLink *link,
                                                      int perms, int w, int h);