Improve pkg/controller/revision/revision.go coverage

[mattmoor]

Move these to a helpers.go, and coverage in helpers_test.go:

• getDeploymentProgressCondition could use focused unit testing,
• getRevisionLastTransitionTime could use focused unit testing,
• getBuildDoneCondition could use focused unit testing,
• isBuildDone could use focused unit testing

addDeploymentProgressEvent needs coverage for most of its body.

removeFinalizers needs coverage for most of its body.

The logger.Errorf before many return err amplifies the lack of coverage along error paths. The runtime.HandleError pattern is similar, but less pronounced (probably not worth a helper).

This path seems easy to cover in addEndpointsEvent:

if revisionAge < serviceTimeoutDuration {
    return
}

[mattmoor]

Once #1166 lands, I think the biggest coverage gap is removeFinalizers, at which point it is likely safe to resolve this.

[mattmoor]

removeFinalizers looks unused, so I'm just removing it: #1173

[mattmoor]

We should be in reasonable shape here.