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 'text/html' in response.headers.get('Content-Type', '') \
                        and not response_content_str.lower().startswith('<!doctype html'):
                    response.headers['Content-Type'] = 'application/xml; charset=utf-8'
                reset_content_length = True
            
            if method == 'DELETE':
                reset_content_length = True
            if reset_content_length:
                response.headers['content-length'] = len(response._content)
    def _update_location(self, content, bucket_name):
        bucket_name = normalize_bucket_name(bucket_name)
        host = config.HOSTNAME_EXTERNAL
        if ':' not in host:
            host = '%s:%s' % (host, config.PORT_S3)
        return re.sub(r'<Location>\s*([a-zA-Z0-9\-]+)://[^/]+/([^<]+)\s*</Location>',
            r'<Location>%s://%s/%s/\2</Location>' % (get_service_protocol(), host, bucket_name),
            content, flags=re.MULTILINE)
    @staticmethod
    def is_query_allowable(method, query):
        
        if not query:
            return True
        
        contains_cred = 'X-Amz-Credential' in query and 'X-Amz-Signature' in query
        contains_key = 'AWSAccessKeyId' in query and 'Signature' in query
        if (method == 'POST' and query.startswith('uploadId')) or contains_cred or contains_key:
            return True
UPDATE_S3 = ProxyListenerS3()