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update vendor spf13/cobra to enforce required flags
**What this PR does / why we need it**:
spf13/cobra#502 has enforced checking flags that marked as required, an error will be raised if unset.
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*:fixes #54855
xref #48400fixeskubernetes/kubectl#121
**Special notes for your reviewer**:
/assign @liggitt @eparis
**Release note**:
```release-note
kubectl now enforces required flags at a more fundamental level
```
This moves plugin/pkg/scheduler to pkg/scheduler and
plugin/cmd/kube-scheduler to cmd/kube-scheduler.
Bulk of the work was done with gomvpkg, except for kube-scheduler main
package.