[protos] Rename UpdateDeviceListForUser RPC to UpdateDeviceList

Summary:
Addresses ENG-6839

The ForUser suffix suffix should be only when request contains [non-caller] user_id

Test Plan: Identity and native compiles

Reviewers: varun, ashoat

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D11378