lavf remove duplicated check in has_duration

this hunk was merged in 8b97ae64 and cbf767a8 although the check was there a
few lines above since cdced09e. I removed the first check to reduce the differences
to libav.

Signed-off-by: Jean First <jeanfirst@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/utils.c

@@ -1977,8 +1977,6 @@ static int has_duration(AVFormatContext *ic)
 {
     int i;
     AVStream *st;
-    if(ic->duration != AV_NOPTS_VALUE)
-        return 1;
 
     for(i = 0;i < ic->nb_streams; i++) {
         st = ic->streams[i];