[TASK] Remove old code from css_styled_content

Some old code inside css_styled_content is unused, old and just
using disk space. Solution: Remove it.

Change-Id: I0ed50512c7b0f5e1906ff329662cb4662188788a
Resolves: #47088
Releases: 6.1
Reviewed-on: https://review.typo3.org/19773
Reviewed-by: Nicole Cordes
Tested-by: Nicole Cordes
Reviewed-by: Georg Ringer
Tested-by: Georg Ringer