Is there anything else on the partition? If not, just connect the drive directly to your Mac and erase the partition with Disk Utilitiy -- that will be much faster.
If there is, connect it directly to your Mac. Deleting the sparse bundle will take quite a while, but be faster if it's connected directly.
Select and right-click the sparse bundle via the Finder, and select Show Package Contents.
On the next window, select and right-click the token and select Get Info. Remove the check from the locked box.
Then try the deletion again.
If it seems excruciatingly slow, see the blue box in #Q5 of Using Time Machine with a Time Capsule.