PixelPaint: Don't update ImageEditor in set_active_layer()

Setting the active layer does not cause anything to render differently.
Thus no update is needed and the call to layers_did_change() is
unnecessary.

Userland/Applications/PixelPaint/ImageEditor.cpp

@@ -420,8 +420,6 @@ void ImageEditor::set_active_layer(Layer* layer)
         if (on_active_layer_change)
             on_active_layer_change({});
     }
-
-    layers_did_change();
 }
 
 void ImageEditor::set_active_tool(Tool* tool)