docs(ec2): remove references to deprecated allowAllTraffic parameter (#18970)

allowAllTraffic is not available in CDK v2 (and it has been deprecated in CDK v1), so the example code snippets should refer to the newer parameter defaultAllowedTraffic instead.

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Author: Chriscbr

packages/@aws-cdk/aws-ec2/README.md

@@ -199,15 +199,16 @@ MachineImage.genericLinux({ ... })` and configure the right AMI ID for the
 regions you want to deploy to.
 
 By default, the NAT instances will route all traffic. To control what traffic
-gets routed, pass `allowAllTraffic: false` and access the
-`NatInstanceProvider.connections` member after having passed it to the VPC:
+gets routed, pass a custom value for `defaultAllowedTraffic` and access the
+`NatInstanceProvider.connections` member after having passed the NAT provider to
+the VPC:
 
 ```ts
 declare const instanceType: ec2.InstanceType;
 
 const provider = ec2.NatProvider.instance({
   instanceType,
-  allowAllTraffic: false,
+  defaultAllowedTraffic: ec2.NatTrafficDirection.OUTBOUND_ONLY,
 });
 new ec2.Vpc(this, 'TheVPC', {
   natGatewayProvider: provider,