Remove unnecessary forward declaration.

Originally committed as revision 11583 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/ac3enc.c

@@ -73,8 +73,6 @@ static int16_t xsin1[128];
 /* new exponents are sent if their Norm 1 exceed this number */
 #define EXP_DIFF_THRESHOLD 1000
 
-static void fft_init(int ln);
-
 static inline int16_t fix15(float a)
 {
     int v;