[CLEANUP beta] Remove deprecate-router-events support code

[xg-wang]

Deprecation https://deprecations.emberjs.com/v3.x/#toc_deprecate-router-events

This PR removes

• OverridingwillTransition and didTransition hooks on EmberRouter
• willTransition and didTransition events on Route

Based on https://github.com/emberjs/rfcs/blob/af64915b5ecde010fce09309a47ee6d2447588d0/text/0095-router-service.md#transition-object I think willTransition and didTransition on Route are not deprecated.
They are triggered from https://github.com/tildeio/router.js/blob/4f5d411e9ba44efea003bc3159484b4060ebfc2a/lib/router/router.ts#L811

[snewcomer]

note ref - #19709

Either one is fine by me!

[xg-wang]

It looks like #19709 removed the deprecation warnings but still triggers those events if app has the route event. But it also appears I missed removing used test code part, I picked those to this PR.

[xg-wang]

@rwjblue I checked the router service RFC and I think actions on Route are not deprecated

[snewcomer]

I'm wondering if we can take this a step further and make defaultDidTransition && defaultWillTransition the defacto method that is called when didTransition/willTransition is called on the PrivateRouter. I'm wondering if we can take everything in, say defaultDidTransition and just throw it in here and then get rid of the assert.

[nlfurniss]

@xg-wang what do you think?

[xg-wang]

@snewcomer @nlfurniss sorry for the late reply.

The problem of putting everything from defaultDidTransition to here is that there won't be assertion thrown when people who used to override the didTransition. Before this PR there are warnings.

My thought is that we should internally migrate from router_js's didTransition to routeDidChange then major bump router_js to remove didTransition/willTransition. Meanwhile keep the defaultDidTransition.

[xg-wang]

Rebased to resolve a conflict