I'm not how many of these tests are worth keeping at all, but as a first
step, let's get them into the main test suite. The runtime of the parallel
group with these tests is about 1 minute on my laptop.

This is mostly a straightforward move, with mechanical changes removing the
useless TINC tags. However, some tests were marked with the special
"@executemode ORCA_PLANNER_DIFF" tag. The code in __init__.py ran those
tests differently. Normally, you run a test, and comparet the output with
the expected output file. But those ORCA_PLANNER_DIFF tests were run twice,
with and without ORCA, and the results were compared against each other,
instead of the expected output stored in the repository. The expected
outputs of those tests were out of date, you got a different error message
now than what was remembered in the expected output.

Now those tests are run as normal pg_regress tests. I updated the expected
output of those tests to match what you get nowadays.