[BUGFIX] Remove indeterministic test ensureCorrectPostOrderingByCategoryTitle

The test only works on MySQL with disabled SQL MODE ONLY_FULL_GROUP_BY.
All standard conformant database setups fail this test as the result of
the query is not deterministic due to GROUP BY being evaluated before
ORDER BY.

Change-Id: Ib6d4599e0f5682e8b72971d0f35ef00cfa8d3e6a
Resolves: #80014
Releases: master, 7.6
Reviewed-on: https://review.typo3.org/51844


Reviewed-by: Thomas Hohn <thomas@hohn.dk>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Johannes Goslar <jogo@kronberger-spiele.de>
Tested-by: Johannes Goslar <jogo@kronberger-spiele.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Morton Jonuschat <m.jonuschat@mojocode.de>
Tested-by: Morton Jonuschat <m.jonuschat@mojocode.de>