provider/aws: fix CheckDestroy for ProtocolPolicy tests
provider/aws: fix CheckDestroy for ProtocolPolicy tests

Can only assert that the load balancer is gone, since the test suite
deletes everything, and the load balancer is the way you get to the
proxy protocol policy.

charles-at-geospock/terraform-provider-aws,kjmkznr/terraform-provider-aws,nbaztec/terraform-provider-aws,ashinohara/terraform-provider-aws,kjmkznr/terraform-provider-aws,ClementCunin/terraform-provider-aws,ashinohara/terraform-provider-aws,terraform-providers/terraform-provider-aws,Ninir/terraform-provider-aws,ClementCunin/terraform-provider-aws,charles-at-geospock/terraform-provider-aws,kjmkznr/terraform-provider-aws,terraform-providers/terraform-provider-aws,kjmkznr/terraform-provider-aws,charles-at-geospock/terraform-provider-aws,ashinohara/terraform-provider-aws,ashinohara/terraform-provider-aws,Ninir/terraform-provider-aws,nbaztec/terraform-provider-aws,nbaztec/terraform-provider-aws,ClementCunin/terraform-provider-aws,terraform-providers/terraform-provider-aws,Ninir/terraform-provider-aws,charles-at-geospock/terraform-provider-aws,Ninir/terraform-provider-aws,nbaztec/terraform-provider-aws,terraform-providers/terraform-provider-aws,ClementCunin/terraform-provider-aws