examples: Drop bogus reference

Canvas doesn't have an "alpha" property.

Change-Id: I7cedff568ec062d7586b6b7333e32a8e52d2e8a9
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

examples/quick/canvas/smile/smile.qml

@@ -97,7 +97,6 @@ Item {
                 ctx.save();
                 ctx.clearRect(0, 0, canvas.width, canvas.height);
                 ctx.translate(originX, originX);
-                ctx.globalAlpha = canvas.alpha;
                 ctx.strokeStyle = canvas.strokeStyle;
                 ctx.fillStyle = canvas.fillStyle;
                 ctx.lineWidth = canvas.lineWidth;