tests/resource/aws_rds_cluster: Fix and standardize TestAccAWSRDSCluster_EncryptedCrossRegionReplication (#14491)
tests/resource/aws_rds_cluster: Fix and standardize TestAccAWSRDSCluster_EncryptedCrossRegionReplication (#14491)

Reference: https://github.com/terraform-providers/terraform-provider-aws/issues/10333
Reference: https://github.com/terraform-providers/terraform-provider-aws/issues/14384

Previously:

```
    TestAccAWSRDSCluster_EncryptedCrossRegionReplication: testing.go:684: Step 0 error: errors during apply:

        Error: error creating RDS cluster: InvalidParameterCombination: Cannot specify database name for cross region replication cluster
```

Output from acceptance testing:

```
--- PASS: TestAccAWSRDSCluster_ReplicationSourceIdentifier_KmsKeyId (1545.00s)
```
terraform-providers/terraform-provider-aws,terraform-providers/terraform-provider-aws,terraform-providers/terraform-provider-aws,terraform-providers/terraform-provider-aws