Don't include boundaries and borders in the background variant

[almccon]

Why do we include the borders in the Terrain Background tiles? There's no good reason for it, and it precludes some kinds of mapping like historical maps or maps of natural phenomena that need to have borders removed. Also, it makes our background tiles unnecessarily unusable for people who need to have different political points-of-view on the map, specifically regarding disputed borders.

Whenever we get around to refreshing the style (perhaps never) we should remove borders from the background, and either put them in their own overlay layer, or just put them in the Terrain Lines variant.

[almccon]

Another comment here: https://twitter.com/iosif_lazaridis/status/1531355163000246272

[ifly6]

I also would encourage having no border in the terrain background tiles. I like to plot maps of the ancient world. Eg https://upload.wikimedia.org/wikipedia/commons/thumb/d/d2/Roman_asia%2C_eve_of_First_Mithridatic_war.svg/800px-Roman_asia%2C_eve_of_First_Mithridatic_war.svg.png. One may note that modern Greece, Bulgaria, Syria, Iraq, etc were not countries with recognised borders 2000 years ago.