ReapSessionOlderThan is a function that locates session entries from the in-memory catalog which have not been referenced before 'possiblyExpired' and deletes them. This is a static function with two implementations, the shard one - owned by the MongoDSessionCatalog, and the router one - owned by the RouterSessionCatalog, and it is needed and only used for the LogicalSessionCache.

The goal of this ticket is to make the function `reapSessionOlderThan` and its implementations be part of the ServiceLiaison (shard and role) and remove it from the SessionCatalog.