Remove call to setText in playground (#3168)

* Remove last instance of setText

tests/playground.html

@@ -237,7 +237,6 @@ function addToolboxButtonCallbacks() {
     for (var i = 0, block; block = blocks[i]; i++) {
       var imageField = block.getField('IMAGE');
       imageField.setValue(src);
-      imageField.setText(image);
     }
   };
   var addVariables = function(button) {