[BUGFIX] TestingToken must not rely on a session
This changes the ``TestingToken`` to implement the
``SessionLessTokenInterface`` so that it doesn't rely on a session
to be started whenever it is authenticated.
This is required in order to make use of the token for CLI based
tests (e.g. from behat).
The change also removes the TestingProviderTest that were actually
outdated and only worked by accident.
Releases: master, 2.2, 2.1