bug: delete on an empty cell shouldn't be in the undo/redo stack

[jimniels]

Hitting "Delete" on a blank cell logs that as an event in the undo stack.

For example, in this gif, I hit the "Delete" key on a cell with a value, then I hit "Delete" on the cells below it, and then hit CMD + Z a number of times and each delete in a blank cell is an event in the stack and it moves the cursor to that cell (which feels weird, I would expect only the first "delete" that actually deleted a value to be in the stack of undos)