Remove duplicated description of --mtu
Remove duplicated description of --mtu

commit baa70e975186bb0ee8a4b16b9374cb6e794f8975 duplicates
the description of --mtu.
This patch removes the duplicated description.

Docker-DCO-1.1-Signed-off-by: Ken ICHIKAWA <ichikawa.ken@jp.fujitsu.com> (github: ichik1)

docker/cli,cpuguy83/cli,Zebrilee/cli,allencloud/cli,allencloud/cli,thaJeztah/cli,redpanda/cli,thaJeztah/cli,e11137/cli,Zebrilee/cli,ashfall/cli,cpuguy83/cli,dnephin/cli,dnephin/cli,e11137/cli,docker/cli,ashfall/cli,redpanda/cli,riyazdf/cli,riyazdf/cli