The DurableCatalog should not be in charge of onCommit handling for index and collection catalog entry deletion. Callers should be.

This and this should be moved out.

This is to improve changes being made in SERVER-49731, wherein we would otherwise need to pass a new Ident (new base class for RecordStore and SDI) class into the DurableCatalog to pass along to the KVDropPendingIdentReaper called in onCommit hooks. The KVDropPendingIdentReaper and Ident classes should be none of the DurableCatalog's business.