Hide early school, kindergarten

[nvkelso]

            school-early:
                filter:
                    kind: [school, kindergarten]
                    any:
                        # show labels for smaller landuse areas at higher zooms
                        - { $zoom: [13], area: { max: 100000 } }
                        - { $zoom: [14], area: { max: 50000 } }
                        - { $zoom: [15], area: { max: 10000 } }
                        - { $zoom: [16], area: { max: 5000 } }
                        - { $zoom: [17], area: { max: 2000 } }
                draw:
                    mapzen_icon_library:
                        visible: false

[nvkelso]

This is already using tier6_min_zoom, which seems like okay logic, but let's split it off to follow the above guidelines instead, and only start at zoom 13, default to 18 when no area.

School, by zoom:

• https://www.openstreetmap.org/way/39335805#map=13/37.7776/-122.4917
• https://www.openstreetmap.org/way/226324839#map=14/37.74764/-122.48013
• https://www.openstreetmap.org/way/162470880#map=15/37.75786/-122.50194
• https://www.openstreetmap.org/way/162470889#map=16/37.7614/-122.5022
  https://www.openstreetmap.org/node/358803287#map=18/37.76986/-122.44519

kindergarden is same general logic, single test should suffice:

• https://www.openstreetmap.org/way/256908810#map=18/37.78281/-122.42791

[nvkelso]

QA verified.