chore: rely on default arg parser behavior (#6413)

Author: jamesgeorge007

packages/@vue/cli/bin/vue.js

@@ -234,10 +234,6 @@ enhanceErrorMessages('optionMissingArgument', (option, flag) => {
 
 program.parse(process.argv)
 
-if (!process.argv.slice(2).length) {
-  program.outputHelp()
-}
-
 function suggestCommands (unknownCommand) {
   const availableCommands = program.commands.map(cmd => cmd._name)