REFACTOR: Test Memory Usage Fixes (#7769)

* Calling `Discourse.reset()` creates a new container
We should run our de-initializers only after acceptance tests,
since initializers are not run outside of acceptance tests anyway,
and the container at this point can be passed properly to the
`teardown()` method.

* Remove `Discourse.reset` from tests
This would cause a new container to be created which leaks many objects.

* `updateCurrentUser` is more accurate than `replaceCurrentUser`

test/javascripts/test_helper.js

@@ -169,15 +169,6 @@ QUnit.testDone(function() {
     });
   });
 
-  Discourse._runInitializer("instanceInitializers", function(
-    name,
-    initializer
-  ) {
-    if (initializer && initializer.teardown) {
-      initializer.teardown();
-    }
-  });
-
   window.MessageBus.unsubscribe("*");
 });