[python-experimental] fixes delete endpoint with no body use case

[spacether]

There is a bug where invoking a delete endpoint with no body is unable to call the rest client self.pool_manager.request method because it doesn't understand how to prepare the request/what to send.

This fixes that bug. The solution is to detect this no body use case and omit sending the body in the request.

• sample endpoint has been added to the spec
• test test_delete_endpoint_without_request_body has been added

Note: these responses also lack content (content type to schema) definitions.

This PR was written for:
#12265

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[spacether]

The content-type should not be assumed. It should be set by body serialization.