resource/aws_ram_resource_share_accepter: Minor PR review feedback changes
resource/aws_ram_resource_share_accepter: Minor PR review feedback changes

Reference: https://github.com/terraform-providers/terraform-provider-aws/pull/11562#pullrequestreview-360384762

Output from acceptance testing:

```
--- PASS: TestAccAwsRamResourceShareAccepter_basic (39.67s)
```

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