Default newPage() to device-ready

Summary:
Ref T9690. The "meta viewport" tag got dropped by accident because of the sort of weird logic on the old flow.

Make the default device-ready, then just turn it off for the tiny number of non-device pages.

Test Plan:

• Verified meta viewport tag appears on normal pages again.
• Verified it doesn't show up on non-mobile pages like Maniphest Reports.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9690

Differential Revision: https://secure.phabricator.com/D14396