avformat/avio{,buf}: deprecate AVIOContext::written

Originally added as a private entry in commit
3f75e5116b, but its grouping with
the comment noting its private state was missed during merging of
the field from Libav (most likely due to an already existing field
in between).

libavformat/aviobuf.c

@@ -22,6 +22,7 @@
 #include "libavutil/bprint.h"
 #include "libavutil/crc.h"
 #include "libavutil/dict.h"
+#include "libavutil/internal.h"
 #include "libavutil/intreadwrite.h"
 #include "libavutil/log.h"
 #include "libavutil/opt.h"
@@ -124,7 +125,11 @@ void ffio_init_context(FFIOContext *ctx,
     ctx->current_type        = AVIO_DATA_MARKER_UNKNOWN;
     ctx->last_time           = AV_NOPTS_VALUE;
     ctx->short_seek_get      = NULL;
+#if FF_API_AVIOCONTEXT_WRITTEN
+FF_DISABLE_DEPRECATION_WARNINGS
     s->written               = 0;
+FF_ENABLE_DEPRECATION_WARNINGS
+#endif
 }
 
 AVIOContext *avio_alloc_context(
@@ -166,7 +171,11 @@ static void writeout(AVIOContext *s, const uint8_t *data, int len)
         } else {
             if (s->pos + len > ctx->written_output_size) {
                 ctx->written_output_size = s->pos + len;
+#if FF_API_AVIOCONTEXT_WRITTEN
+FF_DISABLE_DEPRECATION_WARNINGS
                 s->written = ctx->written_output_size;
+FF_ENABLE_DEPRECATION_WARNINGS
+#endif
             }
         }
     }