Allow the removal of security groups in a VPC without causing UPDATE_COMPLETE_CLEANUP_IN_PROGRESS to be stuck for 40m+ due to ENI association.

I'm sure this isn't news, but I couldn't find an issue to track. Some time ago in my template I defined a local security group like:

```yaml
NoOpSecurityGroup:
Type: AWS::EC2::SecurityGroup
```

Which was associated with a function to force it to have its own ENI. Now I did an update to remove the security group, deployment goes through but it gets stuck cleaning up.

Same issue in other frameworks:
* Serverless Framework: https://github.com/serverless/serverless/issues/5008
* Terraform https://github.com/hashicorp/terraform-provider-aws/issues/10329

I don't know what the solution is here, but having the builds blocked for 40+ minutes on something important makes me pretty nervous.