You can remove the Grade Selector drop down from your Department Picker through the Style applied to your Department Picker.

As a Page Manager:
  1. Navigate to School Website.
  2. Under Website Management>Select Websites > Select Your Site.
  3. Click the Styles tab.
  4. Locate the style being used on your Department Picker, and click Edit. 
  5. From the drop down, select Widgets.
  6. Click the Department Picker icon.
  7. On the Right under the Display channel, un-check Grade Selector.
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