Rename "auto" subcommands to "image"

This means all the sub-subcommands can drop the `image-` prefix,
making them shorter and more fluent.

E.g.,

    flux create image policy

rather than

    flux create auto image-policy

Signed-off-by: Michael Bridgen <michael@weave.works>

cmd/flux/delete_image_policy.go

@@ -0,0 +1,40 @@
+/*
+Copyright 2020 The Flux authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package main
+
+import (
+	"github.com/spf13/cobra"
+
+	imagev1 "github.com/fluxcd/image-reflector-controller/api/v1alpha1"
+)
+
+var deleteImagePolicyCmd = &cobra.Command{
+	Use:   "image-policy [name]",
+	Short: "Delete an ImagePolicy object",
+	Long:  "The delete auto image-policy command deletes the given ImagePolicy from the cluster.",
+	Example: `  # Delete an image policy
+  flux delete auto image-policy alpine3.x
+`,
+	RunE: deleteCommand{
+		names:  imagePolicyNames,
+		object: universalAdapter{&imagev1.ImagePolicy{}},
+	}.run,
+}
+
+func init() {
+	deleteAutoCmd.AddCommand(deleteImagePolicyCmd)
+}