Remove newFromMenu() from SideNav

Summary: Ref T10054. Just simplifying this a bit before I start laying in the new profile menus.

Test Plan:

• Viewed Diviner on desktop and checked the mobile menu.
• Viewed Files on desktop and checked the mobile menu.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10054

Differential Revision: https://secure.phabricator.com/D15015