Consider cleaning up left-overs from the Knative integration

It looks we still have some left-overs from Knative:

• https://gitlab.com/gitlab-org/quality/triage-serverless/-/serverless/functions
• https://gitlab.com/gitlab-org/quality/triage-serverless/-/blob/master/serverless.yml
• https://gitlab.com/gitlab-org/quality/triage-serverless/-/blob/master/config/triage-virtual-service.yaml
• Workloads in the knative-serving namespace: