Update zstd to 1.4.4 with minor performance improvements and clarification on replica error messages

Update zstd to 1.4.4. It has some minor improvements in performance and compression ratio. If you run replicas with different versions of ClickHouse you may see reasonable error messages Data after merge is not byte-identical to data on another replicas. with explanation. These messages are Ok and you should not worry. This change is backward compatible but we list it here in changelog in case you will wonder about these messages. #10663 (alexey-milovidov).