Delete power_polygon.sql

Clean-up old stuff.

layers/power/power_polygon.sql

@@ -1,7 +0,0 @@
-
-CREATE OR REPLACE FUNCTION layer_power(bbox geometry, zoom_level int)
-RETURNS TABLE(geometry geometry, class text, name text) AS $$
-    SELECT geometry, class, name
-    FROM osm_power_polygon
-    WHERE zoom_level >= 10 AND geometry && bbox;
-$$ LANGUAGE SQL IMMUTABLE;