[Mainlining] Remove deprecated endpoint /_matrix/client/unstable/users/info

[giomfo]

During the mainlining of synapse, the specific endpoint /_matrix/client/unstable/users/info has been replaced by /_matrix/client/v1/account_status
- The new request format is described in [MSC3720](matrix-org/matrix-spec-proposals#3720)
- In addition to the MSC, the endpoint also returns an org.matrix.expired field for each user (if the user exists) that indicates whether the user is expired
- For the moment this endpoint is not implemented in Element clients. We should plan its implementation at the sdk level

The endpoint /_matrix/client/unstable/users/info is still available in the current version of synapse deployed in Prod, but it will be unsupported in the next deployed version.

I request here the following changes:
1 - look for each occurrences of the use of this endpoint in Tchap-Android
2 - ask the Ops team to update servers on DEV platform in order to observe if an error is prompted in TchapDev - This will let us know if the application has to be updated before the server update
3 - remove this endpoint implementation in the Tchap specific code
The implementation of the new endpoint will be handled in another issue