lavc: postpone removal of audioconvert and sample_fmt wrappers

Those were moved to libavutil only recently.

libavcodec/version.h

@@ -66,10 +66,10 @@
 #define FF_API_INOFFICIAL       (LIBAVCODEC_VERSION_MAJOR < 53)
 #endif
 #ifndef FF_API_OLD_SAMPLE_FMT
-#define FF_API_OLD_SAMPLE_FMT   (LIBAVCODEC_VERSION_MAJOR < 53)
+#define FF_API_OLD_SAMPLE_FMT   (LIBAVCODEC_VERSION_MAJOR < 54)
 #endif
 #ifndef FF_API_OLD_AUDIOCONVERT
-#define FF_API_OLD_AUDIOCONVERT (LIBAVCODEC_VERSION_MAJOR < 53)
+#define FF_API_OLD_AUDIOCONVERT (LIBAVCODEC_VERSION_MAJOR < 54)
 #endif
 #ifndef FF_API_HURRY_UP
 #define FF_API_HURRY_UP         (LIBAVCODEC_VERSION_MAJOR < 53)