Importing k8s.io/kubernetes causes any go modules that depend on this one to
have some issues. For example, the following happens in a module that depends on
troubleshoot:
```shell
$ go list -modfile=./go.mod -m -json -mod=mod all
go: k8s.io/cloud-provider@v0.0.0: invalid version: unknown revision v0.0.0
go: k8s.io/cluster-bootstrap@v0.0.0: invalid version: unknown revision v0.0.0
go: k8s.io/controller-manager@v0.0.0: invalid version: unknown revision v0.0.0
go: k8s.io/cri-client@v0.0.0: invalid version: unknown revision v0.0.0
go: k8s.io/csi-translation-lib@v0.0.0: invalid version: unknown revision v0.0.0
go: k8s.io/dynamic-resource-allocation@v0.0.0: invalid version: unknown revision v0.0.0
go: k8s.io/endpointslice@v0.0.0: invalid version: unknown revision v0.0.0
go: k8s.io/externaljwt@v0.0.0: invalid version: unknown revision v0.0.0
go: k8s.io/kube-controller-manager@v0.0.0: invalid version: unknown revision v0.0.0
go: k8s.io/kube-proxy@v0.0.0: invalid version: unknown revision v0.0.0
go: k8s.io/kube-scheduler@v0.0.0: invalid version: unknown revision v0.0.0
go: k8s.io/mount-utils@v0.0.0: invalid version: unknown revision v0.0.0
go: k8s.io/pod-security-admission@v0.0.0: invalid version: unknown revision v0.0.0
go: k8s.io/sample-apiserver@v0.0.0: invalid version: unknown revision v0.0.0
```
The only thing being used from k8s.io/kubernetes is a simple utility function,
`TaintExists`. Copy it into pkg/k8sutil to eliminate the need for the import.
Signed-off-by: Adam Wolfe Gordon <awg@upbound.io>
Co-authored-by: Andrew Lavery <laverya@umich.edu>
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