Size of SEI list can be used instead

Clean up Decoding Unit Info SEI

See merge request jvet/VVCSoftware_VTM!2724

Fix syntax element names

See merge request jvet/VVCSoftware_VTM!2723

Clean up and fix Picture Timing SEI

See merge request jvet/VVCSoftware_VTM!2722

Use vector of arrays instead of vector