Disable updater writer throttling by default

We have identified few bugs that blocked compaction performance.
The compactor can now run as fast as updater and hence writer throttling
is useless for now.

Change-Id: I925e2d17ec6363596dd344f81933e723e08564b4
Reviewed-on: http://review.couchbase.org/38649
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Sarath Lakshman <sarath@couchbase.com>
Tested-by: Sarath Lakshman <sarath@couchbase.com>