[FOLLOWUP][TASK] Hide selected items in multipleSideBySide

The original patch introduced some regressions which are fixed now:

- Deletion of multiple items works correctly now
- Inserting items by the Element Browser does not throw an error anymore

Resolves: #76071
Releases: master, 7.6
Change-Id: Ie16a1d404c2f12e6c952dc5022caff08ec6af171
Reviewed-on: https://review.typo3.org/48062


Reviewed-by: Nicole Cordes <typo3@cordes.co>
Tested-by: Nicole Cordes <typo3@cordes.co>
Tested-by: Tomita Militaru <militarutomita@gmail.com>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Daniel Goerz <ervaude@gmail.com>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>