Remove parameter to avoid warning while compiling

Unused parameter: engine
in doAllFailoverLogStats

Change-Id: I1147b458a4486a00f9dd460b1314a467253c3a0c
Reviewed-on: http://review.couchbase.org/33303
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: abhinav dangeti <abhinav@couchbase.com>