Rework transport_description_factory to only have non-DTLS mode for testing, and rewrite tests accordingly. Bug: webrtc:11066, chromium:804275 Change-Id: Ie7d477c4331c975e4e0a3034fbbb749ed9009446 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/336880 Commit-Queue: Harald Alvestrand <hta@webrtc.org> Reviewed-by: Henrik Boström <hbos@webrtc.org> Cr-Commit-Position: refs/heads/main@{#41697}