Removed a call to PostAction#destroy
- #destroy was previously hooked into the callbacks around acts_as_paranoid so
  it was no longer the appropriate choice
- The line that manually set the value of #deleted_at was replaced with
  update_column. update_column is the current recommended attribute updating
  column method.
- Ref: http://apidock.com/rails/ActiveRecord/Persistence/update_column
- Ref: http://apidock.com/rails/ActiveRecord/Persistence/update_attribute
- Kept the call to run the :save callbacks, since update_column skips
  callbacks.