[TASK] Cleanups for CSS Styled Content

* Remove "@todo Define visibility" annotations from the render_*
methods. They are called from TS, they need to be public.
* Remove unused variables from the CssStyledContentController
* Don't pass the constants borderColor and rowSpace to
tt_content.image any more, they are not used there

Resolves: #44965
Releases: 6.1
Change-Id: Ia6ee55754c9af976952274e22c01565f15ec2038
Reviewed-on: https://review.typo3.org/17834
Reviewed-by: Wouter Wolters
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn