I don’t think this is really what you want to do, but to remove a remote repository from your local repository you can do this:
git remote remove <remote-name>
Note that this will only remove the link you have in your local repository, it will not touch anything wherever your remote repository actually is.
If you want to physically delete it there, you have to do it there. This is not something that can—or should—be done from a local repository.