components/baseitem: remove useless children push
These two lines cause a lot of these log messages:
qrc:/org/kde/plasma/private/mobileshell/qml/components/BaseItem.qml:45:5: QML QQuickItem: List didn't append all objects
qrc:/org/kde/plasma/private/mobileshell/qml/components/BaseItem.qml:54:5: QML QQuickItem: List didn't append all objects
Moreover, as far as I can see, a component is pushed into a parent's children list as soon as one sets its parent, like in contentItem.parent = contentItemLoader
.