multiboot: Remove unused variables from multiboot.c
    
    Remove unused variables: mh_mode_type, mh_width, mh_height, mh_depth
    
    Signed-off-by: Jack Schwartz <jack.schwartz@oracle.com>
    Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
    Reviewed-by: Prasad J Pandit <pjp@fedoraproject.org>
    Signed-off-by: Kevin Wolf <kwolf@redhat.com>
    (cherry picked from commit 7a2e43cc96fd017883973caf9ee076ae23a3bebd)
    Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>