Remove version-conditional code from compaction_interval_lens.
Remove version-conditional code from compaction_interval_lens.

The value returned by the Get function is not used in pre-watson
compat mode, but it's ok to do some extra work for the sake of
simplicity.

Change-Id: If8a1f5c0fc24aaeba87edbb5532c7af2cb81f83e
Reviewed-on: http://review.couchbase.org/60510
Tested-by: Aliaksey Artamonau <3c875bcfb3adf2a65b2ae7686ca921e6c9433147@gmail.com>
Reviewed-by: Artem Stemkovski <15a0730a27c69f62ab86f2b6c639fca202166c02@couchbase.com>

ceejatec/ns_server,membase/ns_server,ceejatec/ns_server,ceejatec/ns_server,membase/ns_server,membase/ns_server,membase/ns_server,ceejatec/ns_server,ceejatec/ns_server,membase/ns_server,membase/ns_server,ceejatec/ns_server