Sunset Shared Secred encryption option

### Your use case

#### What would you like to do?
Remove all code that is related with Shared Secred encryption.
#### Why would you like to do it?
If to-device key exchange is performant enough to support large calls this would simplify our codebase and make calls more secure.
#### How would you like to achieve it?
Draft a strategy on how we can leave shared secret encryption. We would need a way to verify users. The invite link would need to contain a join secret so we have an actually more secure system.

### Have you considered any alternatives?

Keep shared secret as a long term solution and continue maintaining it.

### Additional context

_No response_

Start by mapping all code and entry points related to Shared Secret encryption, then review how to-device key exchange currently supports calls. Draft the removal strategy, including user verification and a join secret in invite links; done means the strategy clearly defines the code to remove and the more secure replacement requirements.

Written by the indexing model from the issue text.