Fully remove all mapbox references (next major release)

[emilykl]

• 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

[danielsaaf]

i guess that https://github.com/plotly/plotly.py/blob/196527908749d553d8f03b08b107d14f0470a1df/plotly/figure_factory/_hexbin_mapbox.py

also needs some update within this issue!