No logging, at any level, related to ADB overmem cleaning

As introduced in #2405, there is no logging associated with any of the decisions or actions relating to ADB overmem cleaning.

This makes it impossible to be certain about any of the decisions made, or even if decisions were made, without using a debugger.

When ADB overmem cleaning operates on a subset of the entries for servers authoritative for a zone it takes actions that will undermine all of the work done maintaining SRTT values and can cause the server to behave in non-intuitive ways.

Among other possible effects that are not yet properly characterized.