QtWebKitWidgets should not depend directly on QtQuick

A left-over from the split of the QtWebKit and QtWebKitWidgets libraries
meant that QtWebKitWidgets still linked directly to QtQuick, though it
doesn't use it.

Change-Id: I16ebc0020610ee17edde39dcf0a5caeca15a3ef8
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>