Remove string table

[niloc132]

This would be a breaking change to the wire format, and might not apply to all serialization streams.

Since we already track objects that have already been sent, we don't necessarily need a different mechanism for strings to be tracked in this way. Additionally, when sending as utf8, longs are sent as base64 strings in the main payload (up to 12 bytes) - the only effort being saved is in writing the length of the string before each occurrence.

This is a prerequisite to fully streaming reading of payloads, as otherwise no objects can be read until the full payload is received to resolve the type of the first object.