MB-29548: Remove 'FlusherTask' phosphor trace event
MB-29548: Remove 'FlusherTask' phosphor trace event

Of the ~522K phosphot trace events recorded; 394K are instances of
'FlusherTask' (75%). Additionally, the vast majority of these
FlusherTasks are no-ops - there's only 30K instnaces where there
actually /is/ data to write (as captured by couch-kvstore/commit
events).

As such, remove the FlusherTask event to effectively increase the
number (and time window) of events we can record by 4x.

Change-Id: I29258f288581b2b91367a17b9471116f962ab31d
Reviewed-on: http://review.couchbase.org/93872
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Trond Norbye <60edd2ef23891a753f231b0c6f161dc634079a93@gmail.com>

daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine