[BUGFIX] Only check 'CType' when removing items from NewContentElementWizard

Fix the behavior of keepItems in the NewContentElementWizard to only
remove invalid items based on the CType key. Without this patch any
invalid value in tt_content_defValues would result in the content
element being invisible in the wizard.

Resolves: #76242
Related: #61114
Releases: master, 7.6
Change-Id: I31af8e8e7f095d3af01740165900474d7e05a9a5
Reviewed-on: https://review.typo3.org/48226


Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>