Remove unused declaration

Author: homm

src/libImaging/Imaging.h

@@ -609,10 +609,6 @@ ImagingLibTiffDecode(
 extern int
 ImagingLibTiffEncode(Imaging im, ImagingCodecState state, UINT8 *buffer, int bytes);
 #endif
-#ifdef HAVE_LIBMPEG
-extern int
-ImagingMpegDecode(Imaging im, ImagingCodecState state, UINT8 *buffer, Py_ssize_t bytes);
-#endif
 extern int
 ImagingMspDecode(Imaging im, ImagingCodecState state, UINT8 *buffer, Py_ssize_t bytes);
 extern int