Merge pull request #25914 from lixiaobing10051267/masterSwarmJoinManager

Remove option "--manager" description for swarm_join.md
(cherry picked from commit 7cd88e5ec4fc13e1ded0eb7c565ed299b46c8259)

Signed-off-by: Charles Smith <charles.smith@docker.com>

docs/reference/commandline/swarm_join.md

@@ -87,10 +87,6 @@ name, the default port 2377 will be used.
 
 This flag is generally not necessary when joining an existing swarm.
 
-### `--manager`
-
-Joins the node as a manager
-
 ### `--token string`
 
 Secret value required for nodes to join the swarm