Keep the DeactiveColor from generic vcl style without overriding it
with the Qt5 style.

Change-Id: I10ffdc79e1b6878d27ae13c6394ad50d7470f073
Reviewed-on: https://gerrit.libreoffice.org/64522
Tested-by: Jenkins
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>