Only use Canvas for routing segments

Routing trailers are lagging behind and Canvas by default might have side effects (Plugins)

js/plugin/Heightgraph.js

@@ -63,16 +63,6 @@ BR.Heightgraph = function (map, layersControl, routing, pois) {
             },
         },
 
-        onAdd(map) {
-            // As we're using canvas, initialize an `svg` root that is needed for map marker,
-            // see `Heightgraph._showMapMarker`
-            if (!document.querySelector('.leaflet-overlay-pane svg')) {
-                L.svg().addTo(map);
-            }
-
-            return L.Control.Heightgraph.prototype.onAdd.call(this, map);
-        },
-
         addBelow: function (map) {
             // waiting for https://github.com/MrMufflon/Leaflet.Elevation/pull/66
             // this.width($('#map').outerWidth());