Each element in a block has a Block settings icon which is revealed when you hover over an element. Click the block settings icon to access the Block settings pane. Here's how you can remove one or both buttons:
1. Locate which button (Primary or Secondary) you want to remove. A checkmark will indicate that an element is currently displayed in the block.
2. To remove one of the buttons, uncheck the box for it.
3. Click Save to apply the changes. On mobile, click the floppy disk icon in the top right corner.
To learn more about editing blocks, check out this tutorial.