fixed bug related to the cleanup of files after the buffer is destroyed

[rchhong]

Hi, please forgive me if I misunderstood something, but to my understanding, the purpose of the function cleanup is to remove the temporary files that are used to replace the buffer. For instance, with .ipynb files, an additional .py file is generated and replace the buffer that would contain the .ipynb file.

I am on version 0.9.4 of nvim and I find that this cleanup function throws an error stating that "the delete function does not have enough arguments". After doing some research, I have identified the culprit and found a bug that the cleanup function where the cleanup function actually deletes the .ipynb file instead of the temporary .py file generated.

[GCBallesteros]

Thanks for the PR and good catch!