Revert "Cache centroid"

Causes misplaced labels, suspect due to rounding artifacts.

This reverts commit 5344bdea26.

js/id/core/entity.js

@@ -108,14 +108,6 @@ iD.Entity.prototype = {
         });
     },
 
-    // Returns the centroid of the area, in unprojected coordinates.
-    centroid: function(resolver) {
-        return resolver.transient(this, 'centroid', function() {
-            return iD.Entity.areaPath.projection().invert(
-                iD.Entity.areaPath.centroid(this.asGeoJSON(resolver, true)));
-        });
-    },
-
     hasInterestingTags: function() {
         return _.keys(this.tags).some(function(key) {
             return key != 'attribution' &&

js/id/svg/labels.js

@@ -362,7 +362,8 @@ iD.svg.Labels = function(projection, context) {
         }
 
         function getAreaLabel(entity, width, height) {
-            var centroid = projection(entity.centroid(graph)),
+            var path = d3.geo.path().projection(projection),
+                centroid = path.centroid(entity.asGeoJSON(graph, true)),
                 extent = entity.extent(graph),
                 entitywidth = projection(extent[1])[0] - projection(extent[0])[0],
                 rect;