Remove renderWebsocketOutput and use printWebsocketOutput instead

* The `render` command is not used much
* Originally added with commit 898074be3f
* The `#render` anchor (see findOrCreateRenderElement) was the "Render" button above the editor, nothing was rendered at all if executing code and otherwise it would be included _within_ the button.

app/assets/javascripts/editor/editor.js.erb

@@ -84,16 +84,6 @@ var CodeOceanEditor = {
         }
     },
 
-    findOrCreateRenderElement: function (index) {
-        if ($('#render-' + index).isPresent()) {
-            return $('#render-' + index);
-        } else {
-            var element = $('<div>').attr('id', 'render-' + index);
-            $('#render').append(element);
-            return element;
-        }
-    },
-
     getCardClass: function (result) {
         if (result.file_role === 'teacher_defined_linter') {
             return 'card bg-info text-white'