Automatic merge from submit-queue (batch tested with PRs 52445, 52380, 52516, 52531, 52538). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>..

Remove warning about changes in default token TTLs

**What this PR does / why we need it**:
It was planned for 1.9 cleanup to remove that warning, as change was
done few release cycles ago and users should be already aware of it.

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes kubernetes/kubeadm#346

**Special notes for your reviewer**:

**Release note**:
```release-note
NONE
```