Minor.04 Remove Legacy On Prop

BREAKING CHANGE: remove legacy host-element on prop support in @remix-run/component.

Use the on() mixin instead:

• Old: <button on={{ click() {} }} />
• New: <button mix={[on('click', () => {})]} />

This change removes built-in host on handling from runtime, typing, and host-prop composition. Component-level handle.on(...) remains supported.