Remove stackblitz and codesandbox branches about starter

[Atinux]

I think I am fine keeping these branches to ajust the behavior based on the platforms changes, only not listing them directly since there are made to be opened online, see #16

[Atinux]

Is the v3-vercel necessary as well? or can we simply add the deploy button (both Vercel and Netlify) in the v3 readme?

https://github.com/nuxt/starter/tree/v3-vercel

[pi0]

For codesandbox, we are enabling couple of more options (https://github.com/nuxt/starter/blob/v3-codesandbox/sandbox.config.json) such as redirect loop and default view. Can we add them to codesandbox template for nuxt directly? (We also have a postinstall to avoid caching lockfile)