examples/filtering_audio,video: drop call to avcodec_get_frame_defaults()

The avcodec_get_frame_defaults() function is deprecated and its use
doesn't seem required.

doc/examples/filtering_audio.c

@@ -230,7 +230,6 @@ int main(int argc, char **argv)
         }
 
         if (packet.stream_index == audio_stream_index) {
-            avcodec_get_frame_defaults(frame);
             got_frame = 0;
             ret = avcodec_decode_audio4(dec_ctx, frame, &got_frame, &packet);
             if (ret < 0) {

doc/examples/filtering_video.c

@@ -215,7 +215,6 @@ int main(int argc, char **argv)
             break;
 
         if (packet.stream_index == video_stream_index) {
-            avcodec_get_frame_defaults(frame);
             got_frame = 0;
             ret = avcodec_decode_video2(dec_ctx, frame, &got_frame, &packet);
             if (ret < 0) {