Use a custom definition of equal ImageOverrides

- meta are descriptive, not identifying, so they have no bearing on
  whether two ImageOverrides are equal.

Given that all overrides are created brand fresh during a resolve for
the kbld lock file, there's no need to dedup them (removed call to
UniqueImageOverride()).

pkg/kbld/cmd/resolve.go

@@ -235,8 +235,6 @@ func (o *ResolveOptions) emitLockOutput(conf ctlconf.Conf, resolvedImages *Proce
 			})
 		}
 
-		c.Overrides = ctlconf.UniqueImageOverrides(c.Overrides)
-
 		return c.WriteToFile(o.LockOutput)
 	case o.ImgpkgLockOutput != "":
 		iLock := lockconfig.ImagesLock{

pkg/kbld/config/config.go

@@ -6,7 +6,6 @@ package config
 import (
 	"fmt"
 	"io/ioutil"
-	"reflect"
 
 	semver "github.com/hashicorp/go-version"
 	"github.com/k14s/imgpkg/pkg/imgpkg/lockconfig"
@@ -325,13 +324,21 @@ func (d Config) WriteToFile(path string) error {
 	return nil
 }
 
+// Equal reports whether `this` ImageOverride is equal to `that` ImageOverride.
+//   (`ImageMeta` is descriptive — not identifying — so not part of equality)
+func (this ImageOverride) Equal(that ImageOverride) bool {
+	return this.ImageRef == that.ImageRef &&
+		this.NewImage == that.NewImage &&
+		this.Preresolved == that.Preresolved &&
+		this.TagSelection == that.TagSelection
+}
+
 func UniqueImageOverrides(overrides []ImageOverride) []ImageOverride {
 	var result []ImageOverride
 	for _, override := range overrides {
 		var found bool
 		for _, addedOverride := range result {
-			// using DeepEqual instead of '==' since ImageOverride contains a slice
-			if reflect.DeepEqual(addedOverride, override) {
+			if override.Equal(addedOverride) {
 				found = true
 				break
 			}