In design mode drag the divider to the top of the grid to remove them. To create them there should be a handle just above the scroll bar that you can grab and drag down. If you want to prevent them from being created at design time or run time, set DisplayLayout.MaxRowScrollRegions to 1.
Note that you may also want to set DisplayLayout.MaxColScrollRegions to 1 as well if you don't want either row or col scroll regions. To remove ColScrollRegions, drag the divider to the left of the grid to remove them. There is a handle to the left of the scroll bar if you want to add them back.