[native] Delete the backup date label

Summary:
We don't have this info available. It will be introduced in https://linear.app/comm/issue/ENG-9996/allow-computing-backup-timestamp.

https://linear.app/comm/issue/ENG-9680/create-a-restoration-screen

Depends on D14085

Test Plan: Check how the screen looks without the label.

Reviewers: kamil, angelika

Reviewed By: kamil

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D14163