[identity] Update V1 logout to handle new flow users

Summary:
Addresss ENG-9696.

We want V1 logout to still work for new flows, but with two things:

• Don't update device list server side
• Inform the client that it should use new flows (it already handles the use_new_flow response)

Depends on D14075

Test Plan:

• Register a user
• V1 logout - OK
• Log in again and sign the device list (e.g. perform QR login)
• V1 logout again - The use_new_flow is returned and a message is displayed on client

Reviewers: kamil, varun

Reviewed By: kamil

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D14076