Deleting a non-existent key through s3api's delete-objects should return a valid response..

```
aws s3api delete-objects --bucket my-bucket --delete '{\"Objects\":[{\"Key\":\"my-key\"}]}'
```
Gives...
```
{
    "Deleted": [
        {
            "Key": "my-key"
        }
    ]
}
```

Deleting a non-existent key through s3api's delete-objects on LocalStack returns an error response without any additional information beyond the key.

```
aws s3api delete-objects --bucket my-bucket --delete '{"Objects":[{"Key":"my-key"}]}' --endpoint-url http://localhost:4572
```
Gives...
```
{
    "ResponseMetadata": {
        "HTTPStatusCode": 200,
        "HTTPHeaders": {
            "server": "BaseHTTP/0.6 Python/3.7.5",
            "date": "Fri, 20 Dec 2019 16:02:39 GMT",
            "content-type": "application/xml; charset=utf-8",
            "content-length": "180",
            "access-control-allow-origin": "*",
            "last-modified": "Fri, 20 Dec 2019 16:02:39 GMT",
            "access-control-allow-methods": "HEAD,GET,PUT,POST,DELETE,OPTIONS,PATCH",
            "access-control-allow-headers": "authorization,content-type,content-md5,cache-control,x-amz-content-sha256,x-amz-date,x-amz-security-token,x-amz-user-agent,x-amz-target,x-amz-acl,x-amz-version-id,x-localstack-target,x-amz-tagging",
            "access-control-expose-headers": "x-amz-version-id"
        },
        "RetryAttempts": 0
    },
    "Errors": [
        {
            "Key": "my-key"
        }
    ]
}
```

Deleting an existent key seems to work fine.
'x-amz-id-2': 'eftixk72aD6Ap51TnqcoF8eFidJG9Z/2'  
            },
            's3': {
                's3SchemaVersion': '1.0',
                'configurationId': 'testConfigRule',
                'bucket': {
                    'name': bucket_name,
                    'ownerIdentity': {
                        'principalId': 'A3NL1KOZZKExample'
                    },
                    'arn': 'arn:aws:s3:::%s' % bucket_name
                },
                'object': {
                    'key': file_name,
                    'size': file_size,
                    'eTag': 'd41d8cd98f00b204e9800998ecf8427e',
                    'versionId': version_id,
                    'sequencer': '0055AED6DCD90281E5'
                }
            }
        }]
    }
def queue_url_for_arn(queue_arn):
    if '://' in queue_arn:
        return queue_arn
    sqs_client = aws_stack.connect_to_service('sqs')
    parts = queue_arn.split(':')
    return sqs_client.get_queue_url(QueueName=parts[5],
        QueueOwnerAWSAccountId=parts[4])['QueueUrl']
def send_notifications(method, bucket_name, object_path, version_id):