Improve CLI code and descriptions (#28482)

* Close #28444 
* Actually, it doesn't need to use that trick because it looks like it
is not necessary, no user really needs it
* Remove the hidden (legacy) "doctor" subcommand and update documents
* Fix "actions" usage


![image](3c2b34a7-4f92-4a6c-96fd-9505e413d4ec)

cmd/hook.go

@@ -31,8 +31,8 @@ var (
 	// CmdHook represents the available hooks sub-command.
 	CmdHook = &cli.Command{
 		Name:        "hook",
-		Usage:       "Delegate commands to corresponding Git hooks",
-		Description: "This should only be called by Git",
+		Usage:       "(internal) Should only be called by Git",
+		Description: "Delegate commands to corresponding Git hooks",
 		Before:      PrepareConsoleLoggerLevel(log.FATAL),
 		Subcommands: []*cli.Command{
 			subcmdHookPreReceive,