Small screen responsive issue with Navigation

[lizkhoo-shop]

Issue summary

On smaller screen/browser size, the Navigation menu top item has an extra line when the subnav item is selected. Also, the top level item is duplicated.

Expected behavior

No line on the top item of Navigation and no duplication of top item.

Actual behavior

Steps to reproduce the problem

1. Open Admin
2. Select any navigation item
3. Make your browser window narrow enough to collapse Navigation
4. Reopen Navigation to see the bug

[sophschneider]

This was fixed in #11206. Original issue https://github.com/Shopify/polaris-internal/issues/1220