fix: don't show broken enroll link for staff on invite courses

Non-enrolled staff users were being shown enroll links for courses
that you can't self-enroll for (masters-only, invitation-only, etc).

This fixes the outline page to ignore staff status for that check.

AA-1164

lms/templates/courseware/course_about.html

@@ -5,7 +5,6 @@ from django.utils.translation import gettext as _
 from django.utils.translation import pgettext
 from django.urls import reverse
 from lms.djangoapps.courseware.courses import get_course_about_section
-from lms.djangoapps.courseware.toggles import is_courses_default_invite_only_enabled
 from django.conf import settings
 from six import text_type
 from common.djangoapps.edxmako.shortcuts import marketing_link
@@ -90,7 +89,7 @@ from six import string_types
           <span class="register disabled">
             ${_("Course is full")}
           </span>
-        % elif (is_courses_default_invite_only_enabled() or invitation_only) and not can_enroll:
+        % elif invitation_only and not can_enroll:
           <span class="register disabled">${_("Enrollment in this course is by invitation only")}</span>
         ## Shib courses need the enrollment button to be displayed even when can_enroll is False,
         ## because AnonymousUsers cause can_enroll for shib courses to be False, but we need them to be able to click