devel/kdebindings4, devel/kdesdk4, misc/kdeedu4: re-add USE_KDE4

In r415864, kdeprefix was removed from a whole lot of ports. In a
few cases, USE_KDE4= was removed entirely. There are some combinations
of OPTIONS that can cause build failures because KDE4_VERSION isn't
defined. This fixes it.

PR: 209799
Submitted by: groot@kde.org (kde)