Documentation still reference NRU

As per MB 35210 we should not mention NRU as part of ejection type as NRU algorithm is no longer used. But the documentation https://docs.couchbase.com/server/6.6/learn/buckets-memory-and-storage/memory.html#ejection and https://docs.couchbase.com/server/6.6/cli/cbepctl/set-flush_param.html#description still mentions NRU