Deprecate tt_content field select_key
select_key is not used in the core and should be moved into the compat extension.
[!!!][TASK] Deprecate the field select_key of tt_content
The field `select_key` is not used by the core and
is moved to the EXT:compatibility7.
Reviewed-by: Christian Kuhn <firstname.lastname@example.org>
Tested-by: Christian Kuhn <email@example.com>
Tested-by: TYPO3com <firstname.lastname@example.org>
Reviewed-by: Benni Mack <email@example.com>
Tested-by: Benni Mack <firstname.lastname@example.org>