Remove ClusterChannelProvisioner and Channel from eventing.knative.dev

[Harwayne]

Problem
The ClusterChannelProvisioner and Channel types in eventing.knative.dev are deprecated with messages in 0.8. They should be completely removed by 0.9.

Persona:
Contributor and system integrator.

Exit Criteria
The eventing.knative.dev API has neither the ClusterChannelProvisioner nor the Channel types. Those types are also absent from the code.

Additional context (optional)
The changes can only be submitted after 0.8 is cut.

[akashrv]

Duplicate of #1561
@Harwayne Can we close this one? #1561 is already in 0.9 milestone.

[Harwayne]

@Harwayne Can we close this one? #1561 is already in 0.9 milestone.

#1561 only mentions the ClusterChannelProvisioner, not Channel itself. We can either augment that issue to include Channel too or make this issue just for Channel.

[akashrv]

/milestone v0.9.0
Let's have just one single issue. Since this issue talks about both the channel and the provisioner, I'll close #1561

[capri-xiyue]

/assign capri-xiyue

[akashrv]

Related to #1446
@capri-xiyue , @matzew : Please coordinate the work.

[matzew]

@akashrv for in-memory CCP impl: #1484 (merged)

and Kafka (contrib repo): knative/eventing-contrib#515