Automatic merge from submit-queue (batch tested with PRs 53760, 48996, 51267, 54414). 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>.

Removed compatibality code for kubelet 1.2.

**What this PR does / why we need it**:
The next release is 1.8, it's time to remove the backward compatibility code for kubelet 1.2.

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #48995 

**Release note**:
```release-note
The NodeController will not support kubelet 1.2.
```