Remove operate-source update command

Author: Oreoxmt

dm/dm-manage-source.md

@@ -32,7 +32,7 @@ help operate-source
 ```
 
 ```
-`create`/`update`/`stop`/`show` upstream MySQL/MariaDB source.
+`create`/`stop`/`show` upstream MySQL/MariaDB source.
 
 Usage:
   dmctl operate-source <operate-type> [config-file ...] [--print-sample-config] [flags]
@@ -49,8 +49,6 @@ Global Flags:
 
 + `create`：创建一个或多个上游的数据库源。创建多个数据源失败时，会尝试回滚到执行命令之前的状态
 
-+ `update`：更新一个上游的数据库源
-
 + `stop`：停止一个或多个上游的数据库源。停止多个数据源失败时，可能有部分数据源已成功停止
 
 + `show`：显示已添加的数据源以及对应的 DM-worker

dm/dmctl-introduction.md

@@ -50,7 +50,7 @@ Available Commands:
   list-member     Lists member information
   offline-member  Offlines member which has been closed
   operate-leader  `evict`/`cancel-evict` the leader
-  operate-source  `create`/`update`/`stop`/`show` upstream MySQL/MariaDB source
+  operate-source  `create`/`stop`/`show` upstream MySQL/MariaDB source
   pause-relay     Pauses DM-worker's relay unit
   pause-task      Pauses a specified running task or all (sub)tasks bound to a source
   purge-relay     Purges relay log files of the DM-worker according to the specified filename
@@ -103,7 +103,7 @@ Available Commands:
   list-member     Lists member information
   offline-member  Offlines member which has been closed
   operate-leader  `evict`/`cancel-evict` the leader
-  operate-source  `create`/`update`/`stop`/`show` upstream MySQL/MariaDB source
+  operate-source  `create`/`stop`/`show` upstream MySQL/MariaDB source
   pause-relay     Pauses DM-worker's relay unit
   pause-task      Pauses a specified running task or all (sub)tasks bound to a source
   purge-relay     Purges relay log files of the DM-worker according to the specified filename