tests/provider: Refactor endpoints acceptance testing to match style of resource acceptance testing
tests/provider: Refactor endpoints acceptance testing to match style of resource acceptance testing

Output from acceptance testing:

```
--- PASS: TestAccAWSProvider_Endpoints_Deprecated (1.75s)
--- PASS: TestAccAWSProvider_Endpoints (1.77s)
```

kjmkznr/terraform-provider-aws,terraform-providers/terraform-provider-aws,terraform-providers/terraform-provider-aws,kjmkznr/terraform-provider-aws,terraform-providers/terraform-provider-aws,Ninir/terraform-provider-aws,Ninir/terraform-provider-aws,Ninir/terraform-provider-aws,kjmkznr/terraform-provider-aws,Ninir/terraform-provider-aws,terraform-providers/terraform-provider-aws,kjmkznr/terraform-provider-aws