nvidia: make grubby uninstall args match install args

Signed-off-by: Philip J Perry <phil@elrepo.org>
nvidia: add Requires for sed, used in %preun

sed should always be present but this will help yum to resolve deps if
nvidia packages are installed from a kickstart file or from a 3rd party
repo during installation.

Signed-off-by: Philip J Perry <phil@elrepo.org>