Adjust several log lines

[mattmoor]

Drop two that provide nearly no value that have been copy/pasted around since the early days of Knative controllers.

Reduce the CloudEvents log statement to debug level.

Add a log statement to the path where PipelineRun updates the TaskRun status.

/kind cleanup

Submitter Checklist

As the author of this PR, please check off the items in this checklist:

• Docs included if any changes are user facing
• Tests included if any functionality added or changed
• Follows the commit message standard
• Meets the Tekton contributor standards (including
  functionality, content, code)
• Release notes block below has been filled in or deleted (only if no user facing changes)

Release Notes

NONE

cc @afrittoli (IIRC you care most about things touching CE)

[tekton-robot]

The following is the coverage report on the affected files.
Say /test pull-tekton-pipeline-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/reconciler/pipelinerun/pipelinerun.go	82.8%	82.8%	0.0
pkg/reconciler/taskrun/controller.go	96.0%	95.8%	-0.2

[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: vdemeester

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [vdemeester]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[dlorenc]

/lgtm

[mattmoor]

/retest