chore!: drop jsxPure

[ArnaudBarre]

This is a really niche custom property that is passed down to esbuild. If you need it, set jsxSideEffects: true in the esbuild config directly.

[patak-dev]

Given how small usage this has, this could be done in this major. I think it may not be a bad idea to add a message if jsxPure is defined in the config though to point people to use jsxSideEffects (at least having the message during the next major).