Discussion: Remove support for “on*” attribute and property bindings.

[theengineear]

In general, the default template engine doesn’t want to manage adding event listeners in this way — rather, it wants to leave that sort of thing to the authors’s JS via addEventListener.

We may relax this in the future if no special handling is required to support it (i.e., if it’s completely browser-driven).

https://html.spec.whatwg.org/dev/webappapis.html#event-handler-attributes