kill dead inode flags

There are a few inode flags around that aren't used anywhere, so remove
them.  Also update xfsidbg to display all used inode flags correctly.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <david@fromorbit.com>
Signed-off-by: Niv Sardi <xaiki@sgi.com>