SBA SID obsolete signaling bit

The SBA format is now based only on one DirAC+SPAR mode but a signaling bit to distinguish between both is still present in the SBA SID frame and should be thus removed. See e.g. function ivas_dirac_dec_read_BS():

 /* 1 bit flag for SPAR/DirAC, already read in read format function */
   b = st->bit_stream[( st->next_bit_pos )--];