xfs: remove leftovers of old buffer log items in recovery code

XFS used to support different types of buffer log items long time
ago.  Remove the switch statements checking the log item type in
various buffer recovery helpers that were left over from those days
and the rather useless xlog_recover_do_buffer_pass2 wrapper.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>