With the refactoring of the write path under SERVER-23128, the ops/update.cpp update() method is no longer used* to serve user operations. Please:

1. Remove the OpDebug argument from update()
2. Remove the PlanSummaryStats block.
3. Pass a dummy OpDebug to getExecutorUpdate()

* The one exception is in MapReduce which calls Helpers::upsert() which then calls update() to write output data, with a dummy OpDebug. We don't want to track metrics for this path so not a blocker.