manifest/os: don't change the name based on ostree or not

Let the name reflect the pipeline type, and keep it the same whether or not
the contents is meant to be an OSTree commit or not.

internal/distro/fedora/distro.go

@@ -83,7 +83,7 @@ var (
 		rpmOstree:        true,
 		pipelines:        iotCommitPipelines,
 		buildPipelines:   []string{"build"},
-		payloadPipelines: []string{"ostree-tree", "ostree-commit", "commit-archive"},
+		payloadPipelines: []string{"os", "ostree-commit", "commit-archive"},
 		exports:          []string{"commit-archive"},
 	}
 

internal/manifest/os.go

@@ -112,12 +112,8 @@ func NewOSPipeline(m *Manifest,
 	bootLoader BootLoader,
 	grubLegacy string,
 	kernelName string) *OSPipeline {
-	name := "os"
-	if osTree {
-		name = "ostree-tree"
-	}
 	p := &OSPipeline{
-		BasePipeline:   NewBasePipeline(m, name, buildPipeline, nil),
+		BasePipeline:   NewBasePipeline(m, "os", buildPipeline, nil),
 		osTree:         osTree,
 		osTreeParent:   osTreeParent,
 		osTreeURL:      osTreeURL,