Rename dagger.#DAG to dagger.#Plan

Signed-off-by: Solomon Hykes <solomon@dagger.io>

pkg/dagger.io/dagger/engine/plan.cue

@@ -1,10 +1,7 @@
 package engine
 
-// A deployment plan executed by `dagger up`
-#Plan: #DAG
-
 // A special kind of program which `dagger` can execute.
-#DAG: {
+#Plan: {
 	// Receive inputs from the client
 	inputs: {
 		// Receive directories

pkg/dagger.io/dagger/plan.cue

@@ -4,8 +4,5 @@ import (
 	"dagger.io/dagger/engine"
 )
 
-// A deployment plan executed by `dagger up`
-#Plan: engine.#Plan
-
 // A special kind of program which `dagger` can execute.
-#DAG: engine.#DAG
+#Plan: engine.#Plan