kcms/users: Opt out of frameless scrollview for users list

With frameworks/kdeclarative!91
all ScrollView KCMs are frameless by default. This does not work with
the Users KCM due to its somewhat unusual arrangement of displaying two
pages at once, adjacent to one another. This commit opts it back into
the framed style, which looks better, until such time as the layout can
be adjusted to look good with a frameless style, should this be deemed
desirable.