[Bug Report] output_fn expects incorrect content type

**Link to the notebook**

https://github.com/aws/amazon-sagemaker-examples/blob/main/introduction_to_amazon_algorithms/xgboost_abalone/xgboost_inferenece_script_mode.ipynb

**Describe the bug**
output_fn function fails

```
Traceback (most recent call last):
File "/miniconda3/lib/python3.8/site-packages/flask/app.py", line 2446, in wsgi_app
response = self.full_dispatch_request()
File "/miniconda3/lib/python3.8/site-packages/flask/app.py", line 1951, in full_dispatch_request
rv = self.handle_user_exception(e)
File "/miniconda3/lib/python3.8/site-packages/flask/app.py", line 1820, in handle_user_exception
reraise(exc_type, exc_value, tb)
File "/miniconda3/lib/python3.8/site-packages/flask/_compat.py", line 39, in reraise
raise value
File "/miniconda3/lib/python3.8/site-packages/flask/app.py", line 1949, in full_dispatch_request
rv = self.dispatch_request()
File "/miniconda3/lib/python3.8/site-packages/flask/app.py", line 1935, in dispatch_request
return self.view_functions[rule.endpoint](**req.view_args)
File "/miniconda3/lib/python3.8/site-packages/sagemaker_containers/_transformer.py", line 199, in transform
result = self._transform_fn(
File "/miniconda3/lib/python3.8/site-packages/sagemaker_containers/_transformer.py", line 234, in _default_transform_fn
result = self._output_fn(prediction, accept)
File "/miniconda3/lib/python3.8/site-packages/sagemaker_containers/_functions.py", line 95, in wrapper
six.reraise(error_class, error_class(e), sys.exc_info()[2])
File "/miniconda3/lib/python3.8/site-packages/six.py", line 718, in reraise
raise value.with_traceback(tb)
File "/miniconda3/lib/python3.8/site-packages/sagemaker_containers/_functions.py", line 93, in wrapper
return fn(*args, **kwargs)
File "/opt/ml/code/inference.py", line 54, in output_fn
raise ValueError("Content type {} is not supported.".format(content_type))
```

reason is this line

https://github.com/aws/amazon-sagemaker-examples/blob/main/introduction_to_amazon_algorithms/xgboost_abalone/inference.py#L60

Even the transform function alternative in the notebook doesn't do this check

https://github.com/aws/amazon-sagemaker-examples/blob/main/introduction_to_amazon_algorithms/xgboost_abalone/xgboost_inferenece_script_mode.ipynb?short_path=b1cf1d9#L267

So I think this csv check should be removed from output_fn

**To reproduce**
Just run the notebook

**Logs**
If applicable, add logs to help explain your problem.
You may also attach an `.ipynb` file to this issue if it includes relevant logs or output.

Start with introduction_to_amazon_algorithms/xgboost_abalone/inference.py around the output_fn content-type check, then compare it with the transform function in xgboost_inferenece_script_mode.ipynb. Reproduce the failure by running the linked notebook and confirm the inference response succeeds with the content type used there.

Written by the indexing model from the issue text.