Drop prefixes in property names

[peterqliu]

Namely, fill-,line-,raster-,background-

These prefixes automatically take after the layer's type, and as long as they live on separate layers, are redundant. The other prefixes icon- and text- are necessary, since they can cohabit the same symbol layer.

[jfirebaugh]

Given that we need the prefix for symbol properties, and we might want to use them for a combination stroked and filled "polygon" type layer as well, I think we should keep them universal.

[jfirebaugh]

Keeping these for now.

[1ec5]

Dropping the redundant prefixes would be highly desirable for the iOS and macOS SDKs, where property names are expected to be grammatical: mapbox/mapbox-gl-native#6577 (comment). As of mapbox/mapbox-gl-native#7457, we have to twist the English language in weird ways to ensure that Boolean property names in particular use the right parts of speech.

[lucaswoj]

This issue was moved to mapbox/mapbox-gl-js#4083