pgsql: Improve a bit the tests of pg_walinspect

Improve a bit the tests of pg_walinspect

This commit improves the tests of pg_walinspect on a few things:
- Remove aggregates for queries that should fail. If the code is
reworked in such a way that the behavior of these queries is changed,
we would get more input from them, written this way.
- Expect at least one record reported in the valid queries doing scans
across ranges, rather than zero records.
- Adjust a few comments, for consistency.

Author: Bharath Rupireddy
Discussion: https://postgr.es/m/CALj2ACVaoXW3nJD9zq8E66BEf-phgJfFcKRVJq9GXkuX0b3ULQ@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/4f1882b960596c35d62c78fb44e14913eff49a85

Modified Files
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contrib/pg_walinspect/expected/oldextversions.out | 13 +++++----
contrib/pg_walinspect/expected/pg_walinspect.out | 32 ++++++++++-----------
contrib/pg_walinspect/sql/oldextversions.sql | 13 +++++----
contrib/pg_walinspect/sql/pg_walinspect.sql | 34 +++++++++++------------
4 files changed, 47 insertions(+), 45 deletions(-)