Zombie mz_is_building: false in landuse layer

[nvkelso]

• What did you see? Features in the landuse layer have mz_is_building: false.
• What did you expect to see? That's an internal only attribute not meant for export. It should be dropped.
• What map location are you having problems with? http://vector.dev.mapzen.com/osm/all/16/10471/25342.topojson?api_key=vector-tiles-HqUVidw

Looks like this regression is also present on prod (v0.8 tiles) :\

We originally removed them in v0.5, see: #333.

[nvkelso]

Examples:

{"kind":"university","source":"openstreetmap.org","sort_key":36,"area":1003630,
"mz_is_building":false,"min_zoom":9.0,"id":28965902},"arcs":[[255]]},
{"type":"Polygon","properties":

and

{"kind":"retail","source":"openstreetmap.org","sort_key":41,"area":211777,
"mz_is_building":false,"min_zoom":9.0,"id":147002139},"arcs":[[256]]},
{"type":"Polygon","properties":

[nvkelso]

LGTM