test: EE inheritance without util.inherits()

EventEmitter subclass instances should have their own event handlers,
regardless of whether the subclass was created with `util.inherits()`
or the "traditional" `Sub.prototype = new Super();`.

Test case for #7157
Inherit EE events instead of share them with super

Using simple assignment, `this._events` is lifted from the prototype
and shared among all instances.

Rather than rely on `util.inherits()` to copy the prototype properties
to the subclass instance, we can copy the properties that matter, that way
inheritance can be done without `util.inherits()`.

Fixes #7157