use State.HasResources rather than State.Empty

Destroying a terraform state can't always create an empty state, as
outputs and the root module may remain. Use HasResources to warn about
deleting an environment with resources.

command/env_delete.go

@@ -99,9 +99,9 @@ func (c *EnvDeleteCommand) Run(args []string) int {
 		return 1
 	}
 
-	empty := sMgr.State().Empty()
+	hasResources := sMgr.State().HasResources()
 
-	if !empty && !force {
+	if hasResources && !force {
 		c.Ui.Error(fmt.Sprintf(envNotEmpty, delEnv))
 		return 1
 	}
@@ -128,7 +128,7 @@ func (c *EnvDeleteCommand) Run(args []string) int {
 		),
 	)
 
-	if !empty {
+	if hasResources {
 		c.Ui.Output(
 			c.Colorize().Color(
 				fmt.Sprintf(envWarnNotEmpty, delEnv),