Let the scrollbar follow the app color scheme
TerminalColor::onColorsChanged() used to be called updateScrollbarColors(), now that KColorSchemeManager is integrated in Konsole, users can choose a colour scheme for the whole window widget style, where tabs, scrollbar, findbar, right-click context menu are all the same colour as you'd expect from any KDE application.
This removes dimming of the scrollbar when the "dim when inactive" option is disabled, the scrollbar is part of the window GUI, it should follow the same color scheme.