fftools/sync_queue: use timebase from input frames/packets

They are always properly set now. Avoid a separate timebase-setting
call, which duplicates the knowledge of the timebase being used.

fftools/sync_queue.h

@@ -59,12 +59,6 @@ void       sq_free(SyncQueue **sq);
  */
 int sq_add_stream(SyncQueue *sq, int limiting);
 
-/**
- * Set the timebase for the stream with index stream_idx. Should be called
- * before sending any frames for this stream.
- */
-void sq_set_tb(SyncQueue *sq, unsigned int stream_idx, AVRational tb);
-
 /**
  * Limit the number of output frames for stream with index stream_idx
  * to max_frames.