Fix confusion around reporting operations in progress. (#658)

* Fix confusion around reporting operations in progress.

The SQLite refactor meant rewriting all the SourceTableArray loops to use a
query result iterator instead. Well there is a place for a SourceTableArray
loop still, and that's the pgcopydb list progress thing.

* Fix the table-in-copy SQLite query.

The query was meant to report actual duration and transmitted bytes for each
table in-progress, but the join and sum() operations are creating problems
in the SQLite query and the rest of the progress.c code was not prepared to
benefit from the extra information anyway.

The SQLite problem is that the sum(s.duration), sum(s.bytes) causes a single
row output when the dataset is empty, and the other columns are all set to
NULL. That might be because of the lack of a GROUP BY clause.

Simplify that aspect by removing the extra information for now.