Hide Access Plan > Plan Availability > Members-only settings on Access Plans metabox

[kimcoleman]

Describe the bug
With PMPro and LifterLMS in compatibility mode, plans should not be showing an option to set Plan Availability based on "Memberships" (llms_memberships, not PMPro's levels).

To Reproduce
Steps to reproduce the behavior:

1. Edit a course
2. In the Access Plans metabox, add a plan
3. In the "Plan Availability" box, choose "Members-only".

This should not be possible to set as there are no Memberships set up / allowed when in streamline mode.

Screenshots

Expected behavior
This option on Access Plans should not be available.

We could also consider not to show Access Plans at all if the Course has Require Membership settings.