cleanup some issues with error display

app.go

@@ -230,7 +230,6 @@ func (a *App) Run(arguments []string) (err error) {
 
 	cerr := checkRequiredFlags(a.Flags, set)
 	if cerr != nil {
-		fmt.Fprintln(a.Writer, cerr)
 		ShowAppHelp(context)
 		return cerr
 	}
@@ -361,7 +360,6 @@ func (a *App) RunAsSubcommand(ctx *Context) (err error) {
 
 	cerr := checkRequiredFlags(a.Flags, set)
 	if cerr != nil {
-		fmt.Fprintln(a.Writer, cerr)
 		ShowSubcommandHelp(context)
 		return cerr
 	}

command.go

@@ -137,7 +137,6 @@ func (c Command) Run(ctx *Context) (err error) {
 
 	cerr := checkRequiredFlags(c.Flags, set)
 	if cerr != nil {
-		fmt.Fprintln(context.App.Writer, cerr)
 		ShowCommandHelp(context, c.Name)
 		return cerr
 	}

context.go

@@ -320,7 +320,7 @@ func checkRequiredFlags(flags []Flag, set *flag.FlagSet) requiredFlagsErr {
 		if rf, ok := f.(RequiredFlag); ok && rf.IsRequired() {
 			key := strings.Split(f.GetName(), ",")[0]
 			if !visited[key] {
-				missingFlags = append(missingFlags, f.GetName())
+				missingFlags = append(missingFlags, key)
 			}
 		}
 	}