LUDOC-11 misc: remove pre-2.5 conditional text

LUDOC-11 misc: remove pre-2.5 conditional text

Remove conditional text in the manual for Lustre versions earlier
than 2.5.  It is unlikely that many of the changes in the newer
manual are relevant to such old releases, and they would be better
off using the old manual, if needed.

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I82972511a5a53cae0170d37ec422e0ef2fa7dfce
Reviewed-on: https://review.whamcloud.com/38364
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: James Nunez <jnunez@whamcloud.com>