amazon: Govcloud and China now supports tag on creation

_This issue was originally opened by @rickard-von-essen as hashicorp/packer#6604. It was migrated here as a result of the [Packer plugin split](https://github.com/hashicorp/packer/issues/8610#issuecomment-770034737). The original body of the issue is below._

[Since Jul 5, 2018 all AWS regions, including govcloud and china supports tag on creation for EBS and EC2](https://aws.amazon.com/about-aws/whats-new/2018/07/tag-on-create-for-amazon-ec2-and-amazon-ebs-is-now-available-in-the-aws-govcloud-region/).

This allows us to remove all special code for delayed tagging introduced in hashicorp/packer#5841