EE::ProtectedRef inherits has_many and accepts_nested_attributes_for

What

Prevents EE from overwriting has_many :"#{type}_access_levels" and accepts_nested_attributes_for :"#{type}_access_levels".

Are there points in the code the reviewer needs to double check?

One side effect is that this reintroduces a dependent: destroy, until that is removed in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/13835.

Why

Discussed in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/13693#note_38537325

Relates to

• https://gitlab.com/gitlab-org/gitlab-ce/issues/36013
• https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/13693