ctrl+shift+<
or
On my german keyboard it is: ctrl+< for deleting a line ctrl+> (= ctrl+shift+<) for adding a new line
When adding the list elements and list values, make sure you only add the ones you need, if you need 3 elements in your list don't click on the 4th box in the property palette, this will add one more list element.
If you have a blank element and you want to remove it, the only way is to click on the property without clicking the "More..." button press on the "Inherit" button on the top of the property palette, this will reset the list elements and list values so you can add only the elements you want.
if you still have extra empty option then make sure of these:
1- make pop list item required 2- if its database item ... make sure you have yes on databse item and column name filled 3- make the column in table to have default value like '1'