Remove unnecessary parts from the Mapbox layer example

[tschaub]

As far as I could tell, these view settings are not required by the Mapbox layer example:

• minZoom: 1
• extent: [-Infinity, -20048966.10, Infinity, 20048966.10]
• smoothExtentConstraint: false
• smoothResolutionConstraint: false

In addition, since the render function has access to frameState.viewState, I removed the map.getView() call. Since this will only work with a EPSG:3857 view, I removed the view.getProjection() call. And since the focus of this example is the Mapbox layer, I moved the vector layer to the bottom of the example.

[tschaub]

If #9545 is merged first, I'll remove the extent: [-Infinity, -20048966.10, Infinity, 20048966.10] from the view. If this gets in first, I'll update the other branch to remove the extent (I confirmed that the example works without the extent after the changes in #9545).