fix(SebmGoogleMapCircle): removing circles

Fixes #650
Closes #657

Author: sebholstein

src/core/directives/google-map-circle.ts

@@ -247,6 +247,7 @@ export class SebmGoogleMapCircle implements OnInit, OnChanges, OnDestroy {
   ngOnDestroy() {
     this._eventSubscriptions.forEach(function(s: Subscription) { s.unsubscribe(); });
     this._eventSubscriptions = null;
+    this._manager.removeCircle(this);
   }
 
   /**

src/core/services/managers/circle-manager.ts

@@ -32,6 +32,16 @@ export class CircleManager {
     }));
   };
 
+  /**
+   * Removes the given circle from the map.
+   */
+  removeCircle(circle: SebmGoogleMapCircle): Promise<void> {
+    return this._circles.get(circle).then((c) => {
+      c.setMap(null);
+      this._circles.delete(circle);
+    });
+  }
+
   setOptions(circle: SebmGoogleMapCircle, options: mapTypes.CircleOptions): Promise<void> {
     return this._circles.get(circle).then((c) => c.setOptions(options));
   };