Vercel: Removed restriction to use only predefined width's

[MickL]

For some reason it was not possible to just use any width, instead all width's that want to be used needed to be predefined within image.screens which is related to screen size but not to image width. I removed this restriction.

Fixes #1180

[danielroe]

See https://github.com/nuxt/image/issues/1180#issuecomment-1879198450.