Landuse layer min_zooms too detailed and prevents merging

[nvkelso]

To encourage more feature merging, the min_zoom of features in the landuse layer should always be ints not floats. See 512px sized 13/1705/3108.mvt and 14/3412/6216.mvt where the grass has a tenths place on it's float that prevents feature merging.

Aside: These will also move to a new layer in #2025

Not all of these have float min_zoom now, but all of them should have int min_zoom after.

• natural: wetland (wetland)
• natural: mud (wetland) - this seems odd, isn't is mostly under water?
• landuse: forest – but not all the managed "National Forests" (forest)
• natural: forest – but not all the managed "National Forests" (forest)
• landuse: wood – but not all the managed "National Forests" (forest)
• natural: wood – but not all the managed "National Forests" (forest)
• natural: scrub (scrub) – this is mapped to grassland now, but that's in error
• natural: heath (scrub) – this is mapped to grassland now, but that's in error
• landuse: grass (grassland)
• natural: grassland (grassland)
• landuse: meadow (grassland) - these sometimes have names
• natural: desert (desert)
• natural: bare_rock (desert) - should this be barren?
• natural: sand (desert) - should this be barren?
• natural: shingle (barren)
• natural: scree (barren)
• natural: stone (barren)
• natural: rock (barren)
• natural: glacier (glacier)
• landuse: farm (farmland)
• landuse: farmland (farmland)
• landuse: rural (rural)
• natural: tree_row
• barrier: hedge (there may be special handling for barrier lines to bring over?)