JVET-S0115 aspect 2: rename syntax element in VPS

JVET-S0115 aspect 2 (JVET-S0142 item 4): Change the name and semantics of vps_all_layers_same_num_sublayers_flag (to be vps_default_ptl_dpb_hrd_max_tid_flag) to only control VPS syntax without requiring the number of sublayers to be the same for all layers.