lavf/img2enc: remove redundant option 'updatefirst'

'updatefirst' is an undocumented option redundant to older option 'update'. Since it doesn't serve as a shorthand, this patch removes it.

libavformat/img2enc.c

@@ -104,7 +104,7 @@ static int write_packet(AVFormatContext *s, AVPacket *pkt)
                                           AV_FRAME_FILENAME_FLAGS_MULTIPLE) < 0 &&
                    img->img_number > 1) {
             av_log(s, AV_LOG_ERROR,
-                   "Could not get frame filename number %d from pattern '%s' (either set updatefirst or use a pattern like %%03d within the filename pattern)\n",
+                   "Could not get frame filename number %d from pattern '%s' (either set update or use a pattern like %%03d within the filename pattern)\n",
                    img->img_number, img->path);
             return AVERROR(EINVAL);
         }
@@ -203,7 +203,6 @@ static int query_codec(enum AVCodecID id, int std_compliance)
 #define OFFSET(x) offsetof(VideoMuxData, x)
 #define ENC AV_OPT_FLAG_ENCODING_PARAM
 static const AVOption muxoptions[] = {
-    { "updatefirst",  "continuously overwrite one file", OFFSET(update),  AV_OPT_TYPE_BOOL, { .i64 = 0 }, 0,       1, ENC },
     { "update",       "continuously overwrite one file", OFFSET(update),  AV_OPT_TYPE_BOOL, { .i64 = 0 }, 0,       1, ENC },
     { "start_number", "set first number in the sequence", OFFSET(img_number), AV_OPT_TYPE_INT,  { .i64 = 1 }, 0, INT_MAX, ENC },
     { "strftime",     "use strftime for filename", OFFSET(use_strftime),  AV_OPT_TYPE_BOOL, { .i64 = 0 }, 0, 1, ENC },