Update model names in Explore Machine Learning Models with Explainable AI: Challenge Lab

For the Explore Machine Learning Models with Explainable AI: Challenge Lab, [what-if-tool-challenge.ipynb](https://github.com/GoogleCloudPlatform/training-data-analyst/blob/master/quests/dei/what-if-tool-challenge.ipynb) is used. While creating and deploying models, the model names are given as :


While those that are required for this specific lab are:

If this file is used only in this Challenge Lab, we should update these names.