[BUGFIX] Sysext form uses old TCA

Sysext form overrides TCA for tt_content with some completely outdated
configuration.

Fix this to the new TCA of tt_content.

Resolves: #59837
Releases: 6.3, 6.2
Change-Id: Ic2d1d75b767925755160bd337ec6fdfbddc308ab
Reviewed-on: https://review.typo3.org/31385
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn