Turbotax says I have a K-1 with no entries (because I had a K-1 in the past). But I don't have one. How can I delete this?

Easy fix -  see  How do I delete forms in TurboTax Online? for instructions (if you are using a desktop version of TurboTax, see How do I delete a K-1? ).

After deleting the K-1 and any related worksheets, log out of the program. When you log back in, use the Delete a Form tool (List of Forms in My Return) to confirm the K-1 and any related worksheets have been removed from your return.  

Why does this happen? When you transfer the information from your prior year return, the program automatically includes certain forms in the current year - to make sure you don't forget to update those forms. If a form is no longer required (e.g. K-1s, Schedule C), you have to delete them from the current year.