[TASK] Remove functional workspaces DataHandlerTest

DataHandling::canChangeTtContentInTheWorkspace() is now covered
by DataHandling\Regular\Modify\ActionTest::modifyContent() with
additional assertions. The mentioned test class can be removed.

Resolves: #56805
Releases: 6.2
Change-Id: I968c593f50cd7453db87e1c4fe9e0478cf045381
Reviewed-on: https://review.typo3.org/28288
Reviewed-by: Oliver Hader
Tested-by: Oliver Hader