fix: document-id assertion removed
fix: document-id assertion removed

* since the document id is validated in the constructor, we will remove duplicate checking.

couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios