[TASK] Adjust new TCA type "email"

Some followup adjustments to newly introduced
(#97013) TCA type "email".

- Remove eval "email" check in InputTextElement.
- Align TCA migration with the documentation and
  the functionality in the element, since only "null"
  "unique" and "uniqueInPid" are supported.

Resolves: #97267
Related: #97013
Releases: main
Change-Id: Icfc92c72e4dfebacacfd50b1409bffc97c6eb34e
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/74123


Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>