provider/aws: detach VPN gateway with proper ID

builtin/providers/aws/resource_aws_vpn_gateway.go

@@ -218,7 +218,7 @@ func resourceAwsVpnGatewayDetach(d *schema.ResourceData, meta interface{}) error
 	wait := true
 	_, err := conn.DetachVPNGateway(&ec2.DetachVPNGatewayInput{
 		VPNGatewayID: aws.String(d.Id()),
-		VPCID:        aws.String(d.Get("vpc_id").(string)),
+		VPCID:        aws.String(vpcID.(string)),
 	})
 	if err != nil {
 		ec2err, ok := err.(aws.APIError)

builtin/providers/aws/resource_aws_vpn_gateway_test.go

@@ -192,10 +192,6 @@ resource "aws_vpn_gateway" "foo" {
 `
 
 const testAccVpnGatewayConfigChangeVPC = `
-resource "aws_vpc" "foo" {
-	cidr_block = "10.1.0.0/16"
-}
-
 resource "aws_vpc" "bar" {
 	cidr_block = "10.2.0.0/16"
 }