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.
if method == 'GET' and response.status_code == 404 and parsed.query != 'website':
            s3_client = aws_stack.connect_to_service('s3')
            try:
                
                s3_client.head_bucket(Bucket=bucket_name)
                website_config = s3_client.get_bucket_website(Bucket=bucket_name)
                error_doc_key = website_config.get('ErrorDocument', {}).get('Key')
                if error_doc_key:
                    error_object = s3_client.get_object(Bucket=bucket_name, Key=error_doc_key)
                    response.status_code = 200
                    response._content = error_object['Body'].read()
                    response.headers['content-length'] = len(response._content)
            except ClientError:
                
                pass
        if response:
            reset_content_length = False
            
            append_cors_headers(bucket_name, request_method=method, request_headers=headers, response=response)
            append_last_modified_headers(response=response)
            append_list_objects_marker(method, path, data, response)
            fix_location_constraint(response)
            fix_range_content_type(bucket_name, path, headers, response)
            
            
            if method == 'PUT' and ('X-Amz-Security-Token=' in path or
                    'X-Amz-Credential=' in path or 'AWSAccessKeyId=' in path):
                response._content = ''
                reset_content_length = True