Revert "use LIBAV_LICENSE and LIBAV_VERSION instead of FFMPEG_*"

This reverts commit a03be6e1ba.

libavutil/utils.c

@@ -37,5 +37,5 @@ const char *avutil_configuration(void)
 const char *avutil_license(void)
 {
 #define LICENSE_PREFIX "libavutil license: "
-    return LICENSE_PREFIX LIBAV_LICENSE + sizeof(LICENSE_PREFIX) - 1;
+    return LICENSE_PREFIX FFMPEG_LICENSE + sizeof(LICENSE_PREFIX) - 1;
 }