Add Application::removeDeferredServices method

[ollieread]

This PR adds the Application::removeDeferredServices() method. The Application class already has a series of methods for interacting with deferred services:

• getDeferredServices() - Get all deferred services
• setDeferredServices(array $services) - Overwrite all deferred services
• addDeferredServices(array $services) - Merge an array of services into the current deferred services
• isDeferredService(string $service) - Determine if a service is deferred

Currently, if you wanted to remove a service from the deferred service list, you'd have to do something like so:

$deferredServices = $app->getDeferredServices();

unset($deferredServices['auth.password'], $deferredServices['auth.password.broker']);

$app->setDeferredServices($deferredServices);

This is real code I currently have in a package. This PR adds what I consider to be a missing method, which replaces the above code with the following:

$app->removeDeferredServices(['auth.password', 'auth.password.broker']);

I appreciate that this is an obscure use case, but I figured it's worth a PR for such a simpler method with very little overhead and a tiny footprint.

From my use case, I'm providing a custom binding for auth.password and auth.password.broker, which I'm aware will be hit before those deferred services are overridden. This is simply a way to tidy up, and prevent rare edge cases where they end up being loaded after I've overridden.