QmlProfiler: Centralize redrawing of custom canvas

Don't handle redraw events in QML anymore and instead trigger a redraw
on geometryChange as well as componentComplete from C++. This reduces
redundant code and glitches from forgotten QML event handlers.

Change-Id: I0eadfb54cf8e392152c4d91b83c874b37b1aca96
Reviewed-by: Kai Koehne <kai.koehne@digia.com>

src/plugins/qmlprofiler/qml/TimeDisplay.qml

@@ -38,17 +38,6 @@ Canvas2D {
     property real endTime : 0
     property real timePerPixel: 0
 
-
-    Component.onCompleted: {
-        requestRedraw();
-    }
-    onWidthChanged: {
-        requestRedraw();
-    }
-    onHeightChanged: {
-        requestRedraw();
-    }
-
     Connections {
         target: zoomControl
         onRangeChanged: {