[Prep] EX: Remove the account migration screen

[manuroe]

Description

With SSS, there will be no more a SS proxy in the middle that requires to do a super slow initial v2 /sync for the very first login. We can remove this screen from the app.

Internal discussion

The screen to kill

Acceptance criteria

• The screen does not exist anymore in the code
• The app directly displays the room list

Size estimate

S/M/L

Dependencies

We must release this in EX apps only after the synapse release and global SSS availability on matrix.org.

Out of scope

Subtasks

Android

Beta Give feedback

1. [Task] Remove the account migration screen element-x-android#3292
   T-Task +1
   

iOS

Beta Give feedback

1. [Task] Remove the account migration screen element-x-ios#3146
   T-Task +1