Locate a video in Panopto and hover your cursor under the video title until a row of buttons appear. Click on the Settings button.

The Settings pop-up window will appear. On the Overview tab, scroll down to Discussion.

Deselect the Allow viewers to post comments and Enable public comments by default on this video checkboxes.

Close the Settings popup window by clicking on the close window button, which looks like an X.

Now, when you view the video in your browser, it will no longer have a Discussion tab.