[BUGFIX LTS] remove bad setFactoryFor call

This call *attempted* to avoid setting the `INIT_FACTORY` on items
which did not need it (specifically, it avoided setting it on things
which were not instantiable), but ultimately failed to do. It was
ultimately setting the new `FactoryManager` instance as the
`INIT_FACTORY` value on each instantiable object, which includes
classes and not just class instances, since objects are only treated as
non-instantiable when they explicitly specify `instantiate: false`.

The net was a memory leak: the routing service *class* ended up with an
`INIT_FACTORY` pointing to a `FactoryManager` instance which in turn
always had a `container` on it, which meant that there was a cycle (the
container also referenced the service) and thus a leak. This affects
both tests and FastBoot, where we construct new instances of the
service whenever we call the `visit` API.

packages/@ember/-internals/container/lib/container.ts

@@ -481,10 +481,6 @@ export class FactoryManager<T, C extends FactoryClass | object = FactoryClass> {
     this.madeToString = undefined;
     this.injections = undefined;
     setFactoryFor(this, this);
-
-    if (isInstantiatable(container, fullName)) {
-      setFactoryFor(factory, this);
-    }
   }
 
   toString(): string {