Remove Action Invocation as a Resource Mode

plan.go

diff --git a/plan.go b/plan.go
index a987d17..6158684 100644
--- a/plan.go
+++ b/plan.go
@@ -26,9 +26,6 @@
 
 	// ManagedResourceMode is the resource mode for managed resources.
 	ManagedResourceMode ResourceMode = "managed"
-
-	// For Actions
-	ActionInvocationResourceMode ResourceMode = "action"
 )
 
 // Plan represents the entire contents of an output Terraform plan.