NetDB: Combine ExpireRoutersJob and ExpireLeasesJob
A minor performance enhancement/simplification on my list from early this year, made more important by the new proliferation of subdbs.
Not for 2.4.0 as it would probably disrupt the current subdb work. Also, can't even start on this until the subdb changes are substantially complete, especially #406 (closed).
The two jobs are somewhat redundant as both must iterate through the full netdb; one picks out the routers, the other picks out the leasesets.
However, the two run on different schedules, so a combined job would have to schedule on the minimum time, but would then do leases, routers, or both based on time since last done.