Delete placeholder references that are no longer needed after new reassignment process

Background

A new reassignment process has been implemented that eliminates the need for placeholder references. However, these legacy placeholder references still exist in the database and should be cleaned up.

Current Situation

• Placeholder references remain in the database despite no longer being necessary
• The new reassignment process has been successfully deployed and proven reliable
• These redundant references are taking up unnecessary database space

Requirements

Create a database migration to:

• Delete all placeholder references that are:
  • Associated with placeholder users
  • Listed as having database indexes
  • Overlapping with the new reassignment process
• Preserve references that are:
  • Associated with Import User type
  • Don't have proper database index

Acceptance Criteria

• Database migration successfully removes targeted placeholder references
• References associated with Import User type remain intact
• References without proper database index are preserved
• No disruption to existing functionality