Using DOM renderer; no custom extent for layers

The server does not send CORS headers, so we cannot use the
WebGL renderer. Since the layers use the projection's extent,
it is not necessary to specify the extent.

examples/wms-custom-proj.js

@@ -28,8 +28,7 @@ var layers = new ol.Collection([
           'Pixelmap 1:1000000 / geo.admin.ch</a>')],
       crossOrigin: null,
       params: {'LAYERS': 'ch.swisstopo.pixelkarte-farbe-pk1000.noscale'},
-      projection: epsg21781,
-      extent: extent
+      projection: epsg21781
     })
   }),
   new ol.layer.TileLayer({
@@ -41,13 +40,13 @@ var layers = new ol.Collection([
           'National parks / geo.admin.ch</a>')],
       crossOrigin: null,
       params: {'LAYERS': 'ch.bafu.schutzgebiete-paerke_nationaler_bedeutung'},
-      projection: epsg21781,
-      extent: extent
+      projection: epsg21781
     })
   })
 ]);
 
 var map = new ol.Map({
+  renderer: ol.RendererHint.DOM,
   center: new ol.Coordinate(660000, 190000),
   projection: epsg21781,
   layers: layers,