Fully remove all mapbox references (next major release)

- Remove from `graph_objects`:
  - `go.Choroplethmapbox`
  - `go.Densitymapbox`
  - `go.Scattermapbox`

- Remove from `px`:
  - `px.choropleth_mapbox`
  - `px.density_mapbox`
  - `px.scatter_mapbox`
  - `px.line_mapbox`

- Remove all related tests
- Remove `scattermapbox` key from all templates