sout: remove unused sout_input_t.p_sout

include/vlc_sout.h

@@ -144,8 +144,6 @@ enum sout_mux_query_e
 
 struct sout_input_t
 {
-    sout_instance_t *p_sout;
-
     es_format_t     *p_fmt;
     block_fifo_t    *p_fifo;
 

src/stream_output/stream_output.c

@@ -454,7 +454,6 @@ sout_input_t *sout_MuxAddStream( sout_mux_t *p_mux, es_format_t *p_fmt )
     p_input = malloc( sizeof( sout_input_t ) );
     if( !p_input )
         return NULL;
-    p_input->p_sout = p_mux->p_sout;
     p_input->p_fmt  = p_fmt;
     p_input->p_fifo = block_FifoNew();
     p_input->p_sys  = NULL;