This one is a little wily, so John suggested we post it. Removing a label/value from a dropdown should be super-simple. In Oracle Forms, however, you ought to know the shortcut key:
CTRL + SHIFT + ,
Why that combination? Well, it might look strange in writing, but when you type it, you will notice that “SHIFT + ,” makes a less-than symbol “<". I won't go as far as to say this is completely intuitive, but I hope this helps someone.