helper/schema: Introduce Noop and RemoveFromState

This commit implements reusable functions for when resources have no
need to implement a particular operation:

- Noop - does nothing and returns no error.
- RemoveFromState - sets the resource ID to empty string (removing it
  from state) and returns no error.

helper/schema/resource.go

@@ -384,3 +384,17 @@ func (r *Resource) recordCurrentSchemaVersion(
 	}
 	return state
 }
+
+// Noop is a convenience implementation of resource function which takes
+// no action and returns no error.
+func Noop(*ResourceData, interface{}) error {
+	return nil
+}
+
+// RemoveFromState is a convenience implementation of a resource function
+// which sets the resource ID to empty string (to remove it from state)
+// and returns no error.
+func RemoveFromState(d *ResourceData, _ interface{}) error {
+	d.SetId("")
+	return nil
+}