Fix ol.Size order in ol.renderer.canvas.Map and ol.renderer.webgl.Map

Change to `[width, height]` instead of `[height, width]`.

But since the container size is always `[0, 0]` (the element has not
yet been added to the dom) the size of the canvas should not be set in
the constructor.

edit: removed the `canvasSize_` property and use `[this.canvas_.width, this.canvas_.height]` instead