Complete Atlas deprecation.

Removes the push command and the Atlas post-processor.  Please see our
guide on building immutable infrastructure with Packer on CI/CD for
ideas on implementing these features yourself.
https://www.packer.io/guides/packer-on-cicd/

command/fix_test.go

@@ -5,22 +5,6 @@ import (
 	"testing"
 )
 
-func TestFix_noArgs(t *testing.T) {
-	c := &PushCommand{Meta: testMeta(t)}
-	code := c.Run(nil)
-	if code != 1 {
-		t.Fatalf("bad: %#v", code)
-	}
-}
-
-func TestFix_multiArgs(t *testing.T) {
-	c := &PushCommand{Meta: testMeta(t)}
-	code := c.Run([]string{"one", "two"})
-	if code != 1 {
-		t.Fatalf("bad: %#v", code)
-	}
-}
-
 func TestFix(t *testing.T) {
 	c := &FixCommand{
 		Meta: testMeta(t),

command/plugin.go

@@ -48,7 +48,6 @@ import (
 	alicloudimportpostprocessor "github.com/hashicorp/packer/post-processor/alicloud-import"
 	amazonimportpostprocessor "github.com/hashicorp/packer/post-processor/amazon-import"
 	artificepostprocessor "github.com/hashicorp/packer/post-processor/artifice"
-	atlaspostprocessor "github.com/hashicorp/packer/post-processor/atlas"
 	checksumpostprocessor "github.com/hashicorp/packer/post-processor/checksum"
 	compresspostprocessor "github.com/hashicorp/packer/post-processor/compress"
 	dockerimportpostprocessor "github.com/hashicorp/packer/post-processor/docker-import"
@@ -139,7 +138,6 @@ var PostProcessors = map[string]packer.PostProcessor{
 	"alicloud-import":      new(alicloudimportpostprocessor.PostProcessor),
 	"amazon-import":        new(amazonimportpostprocessor.PostProcessor),
 	"artifice":             new(artificepostprocessor.PostProcessor),
-	"atlas":                new(atlaspostprocessor.PostProcessor),
 	"checksum":             new(checksumpostprocessor.PostProcessor),
 	"compress":             new(compresspostprocessor.PostProcessor),
 	"docker-import":        new(dockerimportpostprocessor.PostProcessor),