Build fix: mark some vars as __unused since they are in the Release build
Build fix: mark some vars as __unused since they are in the Release build

Now that we enable NDEBUG in the Release build of CBForest, assert()
calls get disabled, and that means a few variables don't get used.

amco/couchbase-lite-ios,couchbase/couchbase-lite-ios,brendand/couchbase-lite-ios,amco/couchbase-lite-ios,pegli/couchbase-lite-ios,pellekrogholt/couchbase-lite-ios,gotmyjobs/couchbase-lite-ios,pellekrogholt/couchbase-lite-ios,macoscope/couchbase-lite-ios,alfared/couchbase-lite-ios,pellekrogholt/couchbase-lite-ios,couchbase/couchbase-lite-ios,gotmyjobs/couchbase-lite-ios,brendand/couchbase-lite-ios,ipmobiletech/couchbase-lite-ios,tomco/couchbase-lite-ios,ipmobiletech/couchbase-lite-ios,amco/couchbase-lite-ios,lordkev/couchbase-lite-ios,couchbase/couchbase-lite-ios,lordkev/couchbase-lite-ios,alfared/couchbase-lite-ios,brendand/couchbase-lite-ios,brendand/couchbase-lite-ios,macoscope/couchbase-lite-ios,couchbase/couchbase-lite-ios,brendand/couchbase-lite-ios,tomco/couchbase-lite-ios,pegli/couchbase-lite-ios,Chavenay/couchbase-lite-ios,pegli/couchbase-lite-ios,macoscope/couchbase-lite-ios,ipmobiletech/couchbase-lite-ios,Chavenay/couchbase-lite-ios,tomco/couchbase-lite-ios,couchbase/couchbase-lite-ios,Chavenay/couchbase-lite-ios,alfared/couchbase-lite-ios,alfared/couchbase-lite-ios,gotmyjobs/couchbase-lite-ios,macoscope/couchbase-lite-ios,amco/couchbase-lite-ios,tomco/couchbase-lite-ios,amco/couchbase-lite-ios,lordkev/couchbase-lite-ios,amco/couchbase-lite-ios,amco/couchbase-lite-ios,gotmyjobs/couchbase-lite-ios,pegli/couchbase-lite-ios,lordkev/couchbase-lite-ios,pellekrogholt/couchbase-lite-ios,ipmobiletech/couchbase-lite-ios,couchbase/couchbase-lite-ios