Remove unnecessary row ordering dependency in pg_rewind test suite.

Remove unnecessary row ordering dependency in pg_rewind test suite.

t/002_databases.pl was expecting to see a specific physical order of the
rows in pg_database.  I broke that in HEAD with commit 01e386a325549b77,
but I'd say it's a pretty fragile test methodology in any case, so fix
it in 9.5 as well.