Tony Finch authored Apr 13, 2018 and Mark Andrews committed Jun 05, 2019

Since 2008, the cleaning-interval timer has been documented as
"effectively obsolete" and disabled in the default configuration with
a comment saying "now meaningless".

This change deletes all the code that implements the cleaning-interval
timer, except for the config parser in whcih it is now explicitly
marked as obsolete.

I have verified (using the deletelru and deletettl cache stats) that
named still cleans the cache after this change.