[TASK] Remove legacy styling in Web->Template module

Some values (bgColor4) for rendering the tree in the Web->Template module
are never used, and are removed as they are not in use anymore since TYPO3 v7.

Resolves: #84856
Releases: master
Change-Id: Ie3cd0d1e36de29036dc1442849f7fbd76548fd93
Reviewed-on: https://review.typo3.org/56794


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>