If the target is a link and does not exists, remove it before proceeding
    
    This allows to quickly fix all the git hooks on a pagure instance that
    was, for example, migrated from one python version to another and where
    thus all the symlinks are pointing to the old python version and thus
    dangling.
    
    Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>