Switch from golang/mock to uber-go/mock

See https://github.com/golang/mock#gomock: golang/mock is no longer
maintained, and should be replaced by go.uber.org/mock.

This allows golang/mock to be dropped from the status and vendored
fields in unwanted-dependencies.json.

Signed-off-by: Stephen Kitt <skitt@redhat.com>

hack/unwanted-dependencies.json

@@ -20,6 +20,7 @@
       "github.com/go-openapi/validate": "use k8s.io/kube-openapi/pkg/validation/validate instead",
       "github.com/gogo/googleapis": "depends on unmaintained github.com/gogo/protobuf",
       "github.com/gogo/protobuf": "unmaintained",
+      "github.com/golang/mock": "unmaintained, archive mode",
       "github.com/google/s2a-go": "cloud dependency, unstable",
       "github.com/google/shlex": "unmaintained, archive mode",
       "github.com/googleapis/enterprise-certificate-proxy": "references cloud dependencies",