[FEATURE] Clean up local user data

[tadaspetra]

Clean up task

We have an AgoraUser object, that we use for all users, except for the local user. In agora_settings.dart we use isLocalUserMuted, isLocalVideoDisabled and localUid. It makes sense to use the AgoraUser object here. And only have one variable.

Also just double checking... mainAgoraUser != localUser correct?

From my understanding the mainAgoraUser is the "biggest" user in the floating layout. Sometimes it could be the localUser, but not necessarily?