Remove unused function prototype set_drift_counter_state
Remove unused function prototype set_drift_counter_state

Change-Id: I6e1f620d7eb67722aa6f36adcae4046e616675e2
Reviewed-on: http://review.couchbase.org/97701
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Dave Rigby <a09264da4832c7ff1d3bf1608a19f4b870f93750@couchbase.com>

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