Simplify Slider's MouseArea
Simplify Slider's MouseArea

Change-Id: Ib7bc6a370a4cb2bac34d08f4191cca28b69a7185
Reviewed-by: J-P Nurmi <b84a892f57a298bb5dae653b4e188948a84d5549@digia.com>

drgvond/qtquickcontrols,mizukusak/qtquickcontrols,drgvond/qtquickcontrols,mizukusak/qtquickcontrols,mizukusak/qtquickcontrols,drgvond/qtquickcontrols