remove 'api' property which is unused
remove 'api' property which is unused

mapycz/mapnik-reference,mojodna/mapnik-reference,mojodna/mapnik-reference,gravitystorm/mapnik-reference,mapnik/mapnik-reference,CartoDB/mapnik-reference,mapnik/mapnik-reference,mapycz/mapnik-reference,gravitystorm/mapnik-reference,florianf/mapnik-reference,florianf/mapnik-reference,mapnik/mapnik-reference,CartoDB/mapnik-reference