MDL-79986 course: Remove $CFG->linkcoursesections setting
Currently, the $CFG->linkcoursesections setting was only used
for the Classic theme, to let admins decide whether the section
names in the Navigation block would be linked or not.
Now that the course/section.php page has been created to display
the content of any single section, and a link to this section page
has been added from the main course page to help users to focus
on the section content, it has been decided to remove the setting
$CFG->linkcoursesections because it's not required anymore.