[TASK] Mark render function as deprecated

Render function from SoloFieldContainer class has been
marked as deprecated now. It is not used in core anymore.

Resolves: #76101
Releases: master
Change-Id: I276f6b047b6104863f7f7d6c31a713c4df545fbf
Reviewed-on: https://review.typo3.org/48073


Reviewed-by: Nicole Cordes <typo3@cordes.co>
Tested-by: Nicole Cordes <typo3@cordes.co>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>