warning not good for mixin operations when an API version does not have that operation

See https://github.com/Azure/azure-sdk-for-python/blob/master/sdk/textanalytics/azure-ai-textanalytics/azure/ai/textanalytics/_text_analytics_client.py#L504

This will be an initial fix, since ideally we'll later add more information about in which API version an operation will be available.