Revert "Revert "Revert "Revert "Do not draw background or line in toolbars if the color scheme has no headers group""""

This reverts commit ef234aca.

CCMAIL: uhhadd@gmail.com
CCMAIL: kde@david-redondo.de

This commit was inappropriately reverted with no discussion for the
second time, ignoring the comment recommending against it in
plasma/breeze!82 (comment 190308).

This is a community project and you are not the maintainer. Please do
not revert this again, and also stop reverting changes you disapprove
of without discussion. This is an inappropruate use of your commit
rights and may result in their revocation if you keep doing it.

Further offenses will be reported to the CWG.