snapshot: clean wait callback

- rm unnecessary 'window'
- rm commented out line (ne need to attach canvas to window)

Author: etpinard

src/plot_api/to_image.js

@@ -61,11 +61,12 @@ function toImage(gd, opts) {
                 setTimeout(function() {
                     var svg = Snapshot.toSVG(clonedGd);
 
-                    var canvasContainer = window.document.createElement('div');
-                    var canvas = window.document.createElement('canvas');
+                    var canvasContainer = document.createElement('div'),
+                        canvas = document.createElement('canvas');
 
-                    canvasContainer.appendChild(canvas);
+                    // no need to attach canvas container to DOM
 
+                    canvasContainer.appendChild(canvas);
                     canvasContainer.id = Plotly.Lib.randstr();
                     canvas.id = Plotly.Lib.randstr();
 
@@ -86,6 +87,7 @@ function toImage(gd, opts) {
                     }).catch(function(err) {
                         reject(err);
                     });
+
                 }, delay);
             });
         }

src/snapshot/toimage.js

@@ -38,12 +38,12 @@ function toImage(gd, opts) {
         setTimeout(function() {
             var svg = Plotly.Snapshot.toSVG(clonedGd);
 
-            var canvasContainer = window.document.createElement('div');
-            var canvas = window.document.createElement('canvas');
+            var canvasContainer = document.createElement('div'),
+                canvas = document.createElement('canvas');
 
-            // window.document.body.appendChild(canvasContainer);
-            canvasContainer.appendChild(canvas);
+            // no need to attach canvas container to DOM
 
+            canvasContainer.appendChild(canvas);
             canvasContainer.id = Plotly.Lib.randstr();
             canvas.id = Plotly.Lib.randstr();