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.
bucket_name = normalize_bucket_name(bucket_name)
    lock_config = OBJECT_LOCK_CONFIGS.get(bucket_name)
    status_code = 200
    if not lock_config:
        
        lock_config = {
            'Error': {
                'Code': 'ObjectLockConfigurationNotFoundError',
                'Message': 'Object Lock configuration does not exist for this bucket'
            }
        }
        status_code = 404
    body = xmltodict.unparse(lock_config)
    return requests_response(body, status_code=status_code)
def set_lifecycle(bucket_name, lifecycle):
    bucket_name = normalize_bucket_name(bucket_name)
    
    if isinstance(to_str(lifecycle), six.string_types):
        lifecycle = xmltodict.parse(lifecycle)
    BUCKET_LIFECYCLE[bucket_name] = lifecycle
    return 200
def set_replication(bucket_name, replication):
    bucket_name = normalize_bucket_name(bucket_name)
    
    if isinstance(to_str(replication), six.string_types):
        replication = xmltodict.parse(replication)
    BUCKET_REPLICATIONS[bucket_name] = replication
    return 200
def set_encryption(bucket_name, encryption):