Update directory structure for promotion design models.
    
    - Previously, design models related to promotion were stored inside
      the tcar-models-promo directory. This organization makes the
      repository nonfunctional in its pristine state. This update moves
      design models related to promotion from tcar-models-promo directory
      to Models/Promotion directory in order to make the repository
      functional in its pristine state.
    
    - The COPYING file was removed to avoid duplicated copies of it.