Deprecate client keySizeEstimate and valueSizeEstimate attributes

The core configuration has long ago removed the keySizeEstimate and valueSizeEstimate attributes, using instead a BufferSizePredictor to dynamically estimate the size of the next key/value. ProtostreamMarshaller goes even further and ignores the estimate.

We should stop using keySizeEstimate and valueSizeEstimate on the client as well, and instead use a fixed buffer size (ProtostreamMarshaller uses 512).