[fix]: studio display of ungraded subs.s w/useless due dates

By "useless" due dates I'm specifically talking about due dates which
are erroneously set in the course strucutre, but which don't matter
because the entire course is self-paced, rather than instructor-paced.

JIRA:EDUCATOR-5713

cms/templates/js/course-outline.underscore

@@ -235,7 +235,7 @@ if (is_proctored_exam) {
                         <% } %>
                     </p>
                 </div>
-            <% } else if (xblockInfo.get('due_date') || xblockInfo.get('graded')) { %>
+            <% } else if ((xblockInfo.get('due_date') && !course.get('self_paced')) || xblockInfo.get('graded')) { %>
                 <div class="status-grading">
                     <p>
                         <span class="sr status-grading-label"> <%- gettext('Graded as:') %> </span>