Remove unused columns from security_policies table

The following discussion from !159891 (merged) should be addressed:

• @Andyschoenen started a discussion: (+1 comment)

  Suggestion: Should we remove this in a separate MR? Even though there is no data in the table yet, I'm not sure if removing columns still causes problems if we don't ignore them before.

  We can follow this guide to drop columns and:

  1. In this MR, add ignore_columns %i[actions approval_settings], remove_with: '17.5', remove_after: '2024-10-17' to the model.
  2. Add a remove_column migration in %17.4
  3. Remove ignore_columns in %17.5