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>