Fix remaining usages of REQUIRED_QT_VERSION and KF5_DEP_VERSION
REQUIRED_QT_VERSION and KF5_DEP_VERSION trace their origin back to KF5. But in Plasma, we use QT_MIN_VERSION and KF5_MIN_VERSION instead.
REQUIRED_QT_VERSION and KF5_DEP_VERSION trace their origin back to KF5. But in Plasma, we use QT_MIN_VERSION and KF5_MIN_VERSION instead.