Remove any default implementations from interfaces

[MikeAlhayek]

Sometimes we add a default implementation in interfaces to avoid breaking change. With a major release, we should remove the default implementations and document this as a break change. Here are some of the interfaces that should be modified:

• ILoginFormEvent (Done via Prevent External Users Registration #17050)
• Others

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[hishamco]

FYI there is an interface that has a default implementation for a reason, so we need to remove those who have an implementation to avoid the breaking change at that time

[MikeAlhayek]

I know there is a reason. The reason is started I my issue. In v3 we need to remove the default implementation from the interface and introduce a breaking change.