fftools/ffmpeg: drop a write-only variable

fftools/ffmpeg.c

@@ -3696,7 +3696,6 @@ static void free_input_thread(int i)
         av_packet_free(&pkt);
 
     pthread_join(f->thread, NULL);
-    f->joined = 1;
     av_thread_message_queue_free(&f->in_thread_queue);
 }
 

fftools/ffmpeg.h

@@ -437,7 +437,6 @@ typedef struct InputFile {
     AVThreadMessageQueue *in_thread_queue;
     pthread_t thread;           /* thread reading from this file */
     int non_blocking;           /* reading packets from the thread should not block */
-    int joined;                 /* the thread has been joined */
     int thread_queue_size;      /* maximum number of queued packets */
 } InputFile;