WL-2910 Firstly a course can only be current or previous.
Count how a re-index progresses.
Change "Old Courses" to Previous Courses"

This keeps the terms used in search and browse consistent.
Remove trailing semi-colon
WL-2910 Don't show old courses by default.

Also make new courses a checkbox option.
WL-2910 Remove the unused faceting.

As we don't facet on current/previous courses any more we don't need to include it in our query.