Clean up ancient test style

Many older tests where written in a style like

SELECT '' AS two, i.* FROM INT2_TBL ...

where the first column indicated the number of expected result rows.
This has gotten increasingly out of date, as the test data fixtures
have expanded, so a lot of these don't match anymore and are misleading.
Moreover, this style isn't really necessary, since the psql output
already shows the number of result rows. (Perhaps this was different at
some point?)

I'm proposing to clean all this up by removing all those extra columns.

The patch is very big, so I'm attaching a compressed version. You can
also see a diff oneline:
https://github.com/postgres/postgres/compare/master...petere:test-cleanup