Remove reference to nonexistent 'Add New' button in menus help tab

[DrewAPicture]

In the Menu Management help tab, we reference clicking the 'create a new menu' link or Add New button, the latter of which no longer exists.

I'd guess this was left over from before we added the tabbed UI/ Manage Locations tab in #23770.

This:

If you haven’t yet created any menus, click the ’create a new menu’ link or the Add New button to get started

Should become:

If you haven’t yet created any menus, click the ’create a new menu’ link to get started

Patch attached.

[SergeyBiryukov]

In 24181:

Remove obsolete reference in menus help tab. props DrewAPicture. fixes #24262.