ci(e2e): drop n2c legs until the dmtrcli infra is ready
The n2c legs depended on a placeholder Demeter dmtrcli socket port-forward that isn't wired up yet. Remove them and their artifacts (the two configs, the setup/stop dmtrcli scripts, the socket mount and `continue-on-error` guard) so the suite is all-green and fails honestly on the remaining n2n/aws/u5c legs. Will reintroduce once the dmtrcli infra is in place. Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>