xfs: xfs_trace.c: remove duplicated #include

Remove duplicated #include('s) in
  fs/xfs/linux-2.6/xfs_trace.c

Signed-off-by: Huang Weiyi <weiyi.huang@gmail.com>
Reviewed-by: Dave Chinner <david@fromorbit.com>
Signed-off-by: Alex Elder <aelder@sgi.com>