xfs: Remove the description of nodelaylog mount option from xfs.txt

nodelaylog mount option is removed by commit 93b8a585. But there still be
the description about it in the xfs document. This patch removes it.

Signed-off-by: Satoru Takeuchi <takeuchi_satoru@jp.fujitsu.com>
Reviewed-by: Ben Myers <bpm@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>