Tabulated display for metadata could show nothing rather than b'' when a table has no metadata

[hyanwong]

As mentioned on slack, on a table with no metadata and a blank schema, currently something like the following

print(ts.tables.nodes)
# or
ts._repr_html_()

will return a tabular view with the "metadata" column filled full of b''. I wonder if in this specific case (no metadata in the entire table, no metadata schema) we should simply not display anything at all in that column? This would be less confusing for newcomers, and not be mistaken for anything else, I think.

If there is a metadata schema set (e.g. JSON), then I guess we would do as we currently do and show {} for all metadata entries in a blank table.