[TASK] Remove extended `SchemaManager::getDatabasePlatform()`

`AbstractSchemaManager::getDatabasePlatform()` is deprecated
and will be remove with Doctrine DBAL 4.x. A intermediate
compat method has been added to the extended `SchemaManager`
classes.

Meanwhile, core internal and testing-framework usages has
been modified and the compatibilty methods are superflous
and will not hit the TYPO3 core directly.

It does not make sense to keep that and extension authors
are able to change there code already with TYPO3 v12 the
removal of these compat methods are not-breaking (yet).

This may be breaking some extensions with Doctrine DBAL 4.x
and will be noticed in the Doctrine DBAL 4.x upgrade change
along with the other breaking changes.

Resolves: #102881
Releases: main
Change-Id: I0308d0aa6c657fbb879f143cb48c9adc1e4fa425
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/82527


Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Stefan Bürk <stefan@buerk.tech>