Revert "MDL-34444 course: show section availability info"

Turns out this change was just wrong, we shouldn't be allowing linking
to unaavilable sections. Just show the availability information on the
'index page'

This reverts commit 87a31bb5d8.

course/view.php

@@ -105,7 +105,7 @@
         $coursesections = $modinfo->get_section_info($section, MUST_EXIST);
 
         // Check user is allowed to see it.
-        if (!$coursesections->uservisible && !empty($section->availableinfo)) {
+        if (!$coursesections->uservisible) {
             // Note: We actually already know they don't have this capability
             // or uservisible would have been true; this is just to get the
             // correct error message shown.