SinkBinding matching a subject using labels doesn't update the subject when label is removed

[xtreme-sameer-vohra]

Describe the bug
When a SinkBinding is created with a subject using labels

kn source binding create bind-event-display --subject Service:serving.knative.dev/v1:foo=bar --sink ksvc:event-display

The binding injects expected variables like K_SINK into a Knative Service such as

kn service create hello --image SOME_IMAGE -l foo=bar

When the service is updated to remove the label

kn service update hello  -l foo-

The binding injected variables are still present in the Knative Service

kubectl describe ksvc/hello
.
..
    Spec:
      Container Concurrency:  0
      Containers:
        Env:
          Name:   TARGET
          Value:  World
          Name:   K_SINK
          Value:  http://event-display.default.svc.cluster.local
          Name:   K_CE_OVERRIDES
        Image:    gcr.io/knative-samples/helloworld-go@sha256:5ea96ba4b872685ff4ddb5cd8d1a97ec18c18fae79ee8df0d29f446c5efe5f50
        Name:     user-container

Expected behavior
The binding injected variables are removed when a subject's matching label is no longer present

To Reproduce
See steps above
Knative release version
v0.26.0