remove redundant #include <math.h>

Originally committed as revision 5734 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavutil/common.h

@@ -604,11 +604,6 @@ static always_inline long int lrintf(float x)
     return (int)(rint(x));
 #endif /* __MINGW32__ */
 }
-#else
-#ifndef _ISOC9X_SOURCE
-#define _ISOC9X_SOURCE
-#endif
-#include <math.h>
 #endif /* HAVE_LRINTF */
 
 #endif /* HAVE_AV_CONFIG_H */