You can inactivate multiple skill assessments all at once, rather than inactivating them individually. 
  1. Navigate to Academics > Grades > Grading Setup > Assessment Skills
  2. Click Update multiple statuses
  3. Use the pop up to select which Assessment Skills you would like to inactivate based on the School Year they are NOT used in
  4. Ensure Update status to is set to Inactive
  5. Click Update status