Open command prompt: cmd
Type bcdedit (as Marcos suggested)
You will find the booting partitions (this term doesn't really exist)
Spot the partition that says "Continue with installation" 
as a description
Copy its {identifier} (yeah, that long number)
Finally, type bcdedit /delete {identifier}, 
where in the place of identifier you have to put the identifier you
selected. (Make sure to keep the identifier between braces {..} ).
Type bcdedit to confirm deletion