helper/schema: remove unused field

helper/schema/resource_data.go

@@ -18,11 +18,10 @@ import (
 // The most relevant methods to take a look at are Get, Set, and Partial.
 type ResourceData struct {
 	// Settable (internally)
-	schema  map[string]*Schema
-	config  *terraform.ResourceConfig
-	state   *terraform.InstanceState
-	diff    *terraform.InstanceDiff
-	diffing bool
+	schema map[string]*Schema
+	config *terraform.ResourceConfig
+	state  *terraform.InstanceState
+	diff   *terraform.InstanceDiff
 
 	// Don't set
 	multiReader *MultiLevelFieldReader

helper/schema/schema.go

@@ -223,10 +223,9 @@ func (m schemaMap) Diff(
 	result.Attributes = make(map[string]*terraform.ResourceAttrDiff)
 
 	d := &ResourceData{
-		schema:  m,
-		state:   s,
-		config:  c,
-		diffing: true,
+		schema: m,
+		state:  s,
+		config: c,
 	}
 
 	for k, schema := range m {