Remove misleading test: around_action return false

When an `around_action` does not `yield`, then the corresponding action is *never* executed and the `after_` actions are *never* invoked.

The value returned by the `around_action` does not have any impact on this: an `around_action` can "return" `true`, `false`, or `"pizza"`, but as long as `yield` is not invoked, the corresponding action and after callbacks are not executed.

The test suite for `ActionController::Callbacks` currently includes separate tests to distinguish the cases in which a non-yielding `around_action` returns `true` or `false`.

In my opinion, having such tests is misleading, giving the impression that the returned value might have some sort of impact, while it does not. At least that's the impression I got when I read those tests.

For completeness, the tests were introduced 7 years ago by @NZKoz in e80fabb.