[BUGFIX] Align functional splitting to chunk execution

The check for doing the functional test splitting
script and running the selected chunk used similar
but different minimum chunk value to check against.
Thus the splitting script has not been executed in
all chunk execution contexts.

This patch uses now exactly the same check in the
'Build/Scripts/runTests.sh' like it is defined in
the corresponding docker-compose service config.

Furthermore all previous created functional split
files are now removed to avoid leftovers, which
occured if re-run has lower chunksize defined.

Example which is now properly fixed:

> Build/Scripts/runTests.sh -s functional -c 1/1

Example with partial part files from previous run:

> Build/Scripts/runTests.sh -s functional -c 1/10
> Build/Scripts/runTests.sh -s functional -c 1/8

Resolves: #97283
Releases: main, 11.5, 10.4
Change-Id: Id3a0d1c85540b4e7e46aaea69cf2d96839e8e72e
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/74194


Tested-by: core-ci <typo3@b13.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>