remove unused `using` directive
remove unused `using` directive

lightmare/mapnik,tomhughes/mapnik,mapnik/mapnik,tomhughes/mapnik,tomhughes/mapnik,lightmare/mapnik,mapnik/mapnik,naturalatlas/mapnik,mapnik/mapnik,mapnik/mapnik,naturalatlas/mapnik,tomhughes/mapnik,naturalatlas/mapnik,lightmare/mapnik,naturalatlas/mapnik,lightmare/mapnik