refact: remove unused function (#2413)
refact: remove unused function (#2413)

* removed the function convertExpires from the class. which was used before #2016 and now it is not used.
couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios