you can delete old code if it's completely obsolete. We still have the git history.
In this case it's mostly code duplication and doesn't contain extra information.

(Aside: 
I'm not always sticking to immediately deleting or overwriting old versions of a functions, but mainly when I want to keep the old version around to check against the new refactored version, or when the old version contains useful information or is a more readable implementation, and I don't want to bother digging in the version control history for it.)