Add the missing "delete" link for the Session resource.
Review Request #7021 — Created March 7, 2015 and submitted
The Session resource supports using HTTP DELETE to log out of the session. This link was missing from the links when logged in, due to the default logic only inserting this if there's a model instance to work with. This change adds the missing link.
Unit tests pass.
Verified manually that the link is present when logged in.
Tool: Pyflakes Processed Files: reviewboard/webapi/resources/session.py reviewboard/webapi/tests/test_session.py Tool: PEP8 Style Checker Processed Files: reviewboard/webapi/resources/session.py reviewboard/webapi/tests/test_session.py