Revert "Git nuke alias also deletes remote-tracking branch"

This reverts commit 1a4ad4ba1e5931a2b17fba3400a71c88518b73de.

To delete a remote-tracking branch, you need to specify the remote as
well. E.g. git branch -rd origin/branch_name

This alias doesn't take that into account. So for now, just continue to
prune origin.