I have never been clear whether this does something within JAWS itself (in which case what follows will probably not apply) or if it works with the Define Names command of Excel itself.
If it is working with the Define Name command, I believe you can get rid of them by selecting the row/column you originally selected, hitting CTRL+SHIFT+F3, and when the dialog comes up for Create Names from Selection then uncheck the checkbox(es) checked, and hit OK. I think that will undefine them. It's worth a try, anyway, as the CTRL+SHIFT+F3 is how you initially define them via Excel itself based on what's the selected range.
Brian - Windows 10 Pro, 64-Bit, Version 1909, Build 18363
Tolerance is the positive and cordial effort to understand another's beliefs, practices, and habits without necessarily sharing or accepting them.
~ Joshua Liebman