`compact_incomplete` should only write a symbol list key if the symbol is new

[alexowens90]

Currently, compact_incomplete always writes a symbol list key. This should only be written if finalize_staged_data/compact_incomplete specify that it was a parallel write, if it was a parallel append, but with an (as yet unimplemented) upsert flag set to True, or if it is being called by a tick collector and the symbol is new.