Redirect URL should be cleared from portal session cookie state.

[GrahamDumpleton]

Describe the bug

The session cookie is used to store index_url when handling session activation and later session deletion. The index_url isn't cleared from the session cookie when the session is deleted. This means can have a strange situation where if using a separate custom front end web portal using the REST API which sent user through a workshop, if then separately try and use the training portal web interface, including supplying event access code, it will actually redirect to the last index_url set in the session cookie state rather than allowing you to view the training portal.

Additional information

No response