oplog.cpp contains several file-scoped variables that ought instead exist per instance of ServiceContext. It also contains a few now-unused global variables, which should be removed. This ticket's task is to remove the disused variables and move the remainder into a decoration on the ServiceContext.

The variables to remove are:

• lastSetTimestamp
• newTimestampNotifier

The variables to move to a decoration are:

• _localOplogCollection
• hashGenerator
• newOpMutex
• _oplogCollectionName