Ideally migrations should be independent of the application code. To that end, could you define a minimal local class for `SupportedPermission` and another for `Permission`? Something like this:
```ruby
class RemoveSupportAppErtpPermission < ActiveRecord::Migration
  class SupportedPermission < ActiveRecord::Base; end
  class Permission < ActiveRecord::Base
    serialize :permissions, Array
  end
end
...
```