Revert "MB-8348:added internal setting for use of fadvise in db compactor"

This reverts commit cbafc776e478174e027ea97b02af12266d182d04.

MB-8348 is reverted because it was confirmed that couchstore
optimization indeed regressed some rebalance use cases.

Conflicts:
	priv/public/index.html

Change-Id: I717b0022d0d154eb0be9d7552dcf606f89d2229a
Reviewed-on: http://review.couchbase.org/26691
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>