Clean up airport maps

[palewire]

Fixes #2629 by cutting a duplicate map and reframing the airports map more clearly as our best, most direct point map example.

[mattijn]

I agree on the lack of diversity on the maps! But I think the techniques behind these approaches are quite different. Especially when reading the related PR: #1407 and issue: #1366 of https://altair-viz.github.io/gallery/airports_count.html.

Instead of deleting, we should improve the title and description to reflect more the goal and technique of the chart.

[palewire]

I've added it back in with a more specific name

[mattijn]

Great!