Remove conditional M_PI definition, it is already defined in

libavutil/mathematics.h indirectly included by libavformat/avformat.h.

Originally committed as revision 21388 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/output-example.c

@@ -27,10 +27,6 @@
 #include <string.h>
 #include <math.h>
 
-#ifndef M_PI
-#define M_PI 3.14159265358979323846
-#endif
-
 #include "libavformat/avformat.h"
 #include "libswscale/swscale.h"