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# Type of request: This is a ...

[x] bug report
[ ] feature request

# Detailed description

SNS is unable to forward the message to SQS (non fifo queue) when using the `elasticmq` backend and fails with the following log
```
2021-01-19T09:31:50:WARNING:localstack.services.sns.sns_listener: Unable to forward SNS message to SQS: An error occurred (InvalidParameterValue) when calling the SendMessage operation: Value for parameter MessageGroupId is invalid. The request include parameter that is not valid for this queue type Traceback (most recent call last):

File "/opt/code/localstack/localstack/services/sns/sns_listener.py", line 297, in message_to_subscribers

sqs_client.send_message(

File "/opt/code/localstack/.venv/lib/python3.8/site-packages/botocore/client.py", line 357, in _api_call

return self._make_api_call(operation_name, kwargs)

File "/opt/code/localstack/.venv/lib/python3.8/site-packages/botocore/client.py", line 676, in _make_api_call

raise error_class(parsed_response, operation_name)

botocore.exceptions.ClientError: An error occurred (InvalidParameterValue) when calling the SendMessage operation: Value for parameter MessageGroupId is invalid. The request include parameter that is not valid for this queue type
```
This is likely a regression due to #3435. Tested with the default backend on `0.12.5` and it works as expected. Also works with `elasticmq` backend on `0.12.4`

## Expected behavior

Same behavior with the `elasticmq` backend as with the default backend.

## Actual behavior

Fails on `elasticmq` backend, no SQS message received when SNS message is sent.

# Steps to reproduce

## Command used to start LocalStack

```yaml
  localstack:
    image: localstack/localstack:0.12.5
    ports:
      - 4566:4566
    environment:
      - AWS_DEFAULT_REGION=ap-northeast-1
      - SERVICES=sns,sqs
      - SQS_PROVIDER=elasticmq
```

## Client code (AWS SDK code snippet, or sequence of "awslocal" commands)
N.A.

attr_name = req_data['AttributeName'][0]
                attr_value = req_data['AttributeValue'][0]
                sub[attr_name] = attr_value
                return make_response(req_action)
            elif req_action == 'GetSubscriptionAttributes':
                sub = get_subscription_by_arn(req_data['SubscriptionArn'][0])
                if not sub:
                    return make_error(message='Unable to find subscription for given ARN', code=400)
                content = '<Attributes>'
                for key, value in sub.items():
                    content += '<entry><key>%s</key><value>%s</value></entry>\n' % (key, value)
                content += '</Attributes>'
                return make_response(req_action, content=content)
            elif req_action == 'Subscribe':
                if 'Endpoint' not in req_data:
                    return make_error(message='Endpoint not specified in subscription', code=400)
            elif req_action == 'ConfirmSubscription':
                if 'TopicArn' not in req_data:
                    return make_error(message='TopicArn not specified in confirm subscription request', code=400)
                if 'Token' not in req_data:
                    return make_error(message='Token not specified in confirm subscription request', code=400)
                do_confirm_subscription(req_data.get('TopicArn')[0], req_data.get('Token')[0])
            elif req_action == 'Unsubscribe':
                if 'SubscriptionArn' not in req_data:
                    return make_error(message='SubscriptionArn not specified in unsubscribe request', code=400)
                do_unsubscribe(req_data.get('SubscriptionArn')[0])
            elif req_action == 'DeleteTopic':
                do_delete_topic(topic_arn)
            elif req_action == 'Publish':
                if req_data.get('Subject') == ['']: