Bugfix/3623 teardown test data properly

Token expiry

So the #create and #update actions were not needed anymore. Also removed the tests

We have a lot of things that act upon a user record and one or more of it's identities at the same time:
* Sing up: Create a user and it's initial identity
* Rename:  Change the username and create a new identity, turn old into an alias
* Cancel Account: Remove user and all their identities.

In order to keep the User and Identity behaviour isolated but still have a this logic represented in a sinle place the Account model deals with all these things.

We could have overwritten the User#create, User#update and User#destroy methods instead. But then we would always create identities, even if we only need a user (for example in tests).

This way the failed stubbing errors were more telling

This way we can stub the token to return the user directly. Stubbing User.find_by_param is not a good idea as it will make all calls to User#find_by_param with a different id fail.