docs: remove npm@6 commands (#14240)

Author: sapphi-red

docs/guide/index.md

@@ -66,9 +66,6 @@ Then follow the prompts!
 You can also directly specify the project name and the template you want to use via additional command line options. For example, to scaffold a Vite + Vue project, run:
 
 ```bash
-# npm 6.x
-npm create vite@latest my-vue-app --template vue
-
 # npm 7+, extra double-dash is needed:
 npm create vite@latest my-vue-app -- --template vue
 

packages/create-vite/README.md

@@ -28,9 +28,6 @@ Then follow the prompts!
 You can also directly specify the project name and the template you want to use via additional command line options. For example, to scaffold a Vite + Vue project, run:
 
 ```bash
-# npm 6.x
-npm create vite@latest my-vue-app --template vue
-
 # npm 7+, extra double-dash is needed:
 npm create vite@latest my-vue-app -- --template vue