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':
                return get_cors(bucket)
            if method == 'PUT':
                return set_cors(bucket, data)
            if method == 'DELETE':
                return delete_cors(bucket)
        if query == 'lifecycle' or 'lifecycle' in query_map:
            if method == 'GET':
                return get_lifecycle(bucket)
            if method == 'PUT':
                return set_lifecycle(bucket, data)
        if query == 'replication' or 'replication' in query_map:
            if method == 'GET':
                return get_replication(bucket)
            if method == 'PUT':
                return set_replication(bucket, data)
        if query == 'encryption' or 'encryption' in query_map:
            if method == 'GET':
                return get_encryption(bucket)
            if method == 'PUT':
                return set_encryption(bucket, data)
        if query == 'object-lock' or 'object-lock' in query_map:
            if method == 'GET':
                return get_object_lock(bucket)
            if method == 'PUT':
                return set_object_lock(bucket, data)
        if modified_data is not None:
            return Request(data=modified_data, headers=headers, method=method)
        return True
    def get_201_reponse(self, key, bucket_name):