[BUGFIX] RTE styling does not fit to TCEforms styling

The toolbar on top still has old background color and border.
Removing these options makes the toolbar better
natively integrated into the rest of the CMS.

Resolves: #57292
Releases: 6.3, 6.2
Change-Id: I51ed27bff09e6b0479aa0673c65497e08b52540c
Reviewed-on: http://review.typo3.org/28767
Reviewed-by: Tymoteusz Motylewski <t.motylewski@gmail.com>
Tested-by: Tymoteusz Motylewski <t.motylewski@gmail.com>
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>