Remove ViewStorageController::loadMultiple()

Now that #2082117: Install default config only when the owner and provider modules are both enabled has landed, I think we can just remove our loadMultiple() method in the ViewStorageController, as now default config will only get installed if both the owner and provider are enabled. So we can (finally) remove the module exists check...

There was an issue for this a very long time ago, but I just couldn't find it, so opened a new one :/