lavfi: remove ff_poll_frame().

It is never used.

libavfilter/avfilter.c

@@ -467,24 +467,6 @@ static int ff_request_frame_to_filter(AVFilterLink *link)
     return ret;
 }
 
-int ff_poll_frame(AVFilterLink *link)
-{
-    int i, min = INT_MAX;
-
-    if (link->srcpad->poll_frame)
-        return link->srcpad->poll_frame(link);
-
-    for (i = 0; i < link->src->nb_inputs; i++) {
-        int val;
-        if (!link->src->inputs[i])
-            return AVERROR(EINVAL);
-        val = ff_poll_frame(link->src->inputs[i]);
-        min = FFMIN(min, val);
-    }
-
-    return min;
-}
-
 static const char *const var_names[] = {
     "t",
     "n",

libavfilter/internal.h

@@ -289,15 +289,6 @@ static inline int ff_insert_outpad(AVFilterContext *f, unsigned index,
                   &f->output_pads, &f->outputs, p);
 }
 
-/**
- * Poll a frame from the filter chain.
- *
- * @param  link the input link
- * @return the number of immediately available frames, a negative
- * number in case of error
- */
-int ff_poll_frame(AVFilterLink *link);
-
 /**
  * Request an input frame from the filter at the other end of the link.
  *