Robert, what Dan described was the app setting, so that no raster layers are ever stretched with a contrast stretch by default - on that particular machine. If that is what you wanted, then Dan nailed it.
If you were only looking to have no contrast stretch on specific raster datasets, you can edit the Dataset Properties (In the Catalog Pane, right-click the dataset in question, and choose Properties). Scroll down to Source Type, and choose Processed. This will now make it so anyone who uses this dataset (regardless of the machine) will see no contrast stretch.