xfs: kill time.h

The typedef for timespecs and nanotime() are completely unnecessary,
and delay() can be moved to fs/xfs/linux.h, which means this file
can go away.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>