[BUGFIX] Create only minimum TCA when adding new palettes

[BUGFIX] Create only minimum TCA when adding new palettes

When adding a new palette to TCA the types::showitem part is modified.
This patch ensures that no empty values are set to the field definitions
as this would trigger the TCA Migrator.

Resolves: #67327
Releases: master
Change-Id: I30cb6a7d6f325705528d1f3c2961e2620068f057
Reviewed-on: http://review.typo3.org/40042
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Frederic Gaus <frederic.gaus@flagbit.de>
Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Andreas Fernandez <typo3@scripting-base.de>