Adds CHANGELOG entries for zendframework#546

Removes the zendframework#543 entry indicating the changed `NotFoundDelegate`,
instead adding a "Removed" entry for that class.

Updates the "Changed" entry for the `NotFoundMiddleware` to indicate its
new constructor arguments.

CHANGELOG.md

@@ -97,18 +97,19 @@ All notable changes to this project will be documented in this file, in reverse
 
   and removes the dependency http-interop/http-server-middleware.
 
-- [#543](https://github.com/zendframework/zend-expressive/pull/543) renames
+- [#543](https://github.com/zendframework/zend-expressive/pull/543) and
+  [#546](https://github.com/zendframework/zend-expressive/pull/546) renames the
   `Zend\Expressive\Middleware\NotFoundHandler` to
   `Zend\Expressive\Middleware\NotFoundMiddleware`, and its accompanying factory
   `Zend\Expressive\Container\NotFoundHandlerFactory` to
-  `Zend\Expressive\Container\NotFoundMiddlewareFactory`.
+  `Zend\Expressive\Container\NotFoundMiddlewareFactory`. Additionally, the
+  class now does the work of the former `Zend\Expressive\Delegate\NotFoundDelegate`,
+  and, as such, accepts the following constructor arguments:
 
-- [#543](https://github.com/zendframework/zend-expressive/pull/543) renames
-  `Zend\Expressive\Delegate\NotFoundDelegate` to
-  `Zend\Expressive\Handler\NotFoundHandler`, updating it to implement the PSR-15
-  `RequestHandlerInterface`. It also renames the factory
-  `Zend\Expressive\Container\NotFoundDelegateFactory` to
-  `Zend\Expressive\Container\NotFoundHandlerFactory`.
+  - PSR-7 `ResponseInterface $responsePrototype` (required)
+  - `Zend\Expressive\Template\TemplateRendererInterface $renderer` (optional)
+  - `string $template = self::TEMPLATE_DEFAULT` (optional; defaults to "error::404")
+  - `string $layout = self::LAYOUT_DEFAULT` (optional; defaults to "layout::default")
 
 - [#543](https://github.com/zendframework/zend-expressive/pull/543) refactors
   `Zend\Expressive\Application` completely.
@@ -187,6 +188,13 @@ All notable changes to this project will be documented in this file, in reverse
 - [#543](https://github.com/zendframework/zend-expressive/pull/543) removes
   support for http-interop/http-server-middleware.
 
+- [#546](https://github.com/zendframework/zend-expressive/pull/546) removes the
+  class `Zend\Expressive\Delegate\DefaultDelegate`, as there is no longer a
+  concept of a default handler invoked by the application. Instead, developers
+  MUST pipe middleware at the innermost layer of the pipeline guaranteed to
+  return a response; we recommend using `Zend\Expressive\Middleware\NotFoundMiddleware` 
+  for this purpose.
+
 - [#543](https://github.com/zendframework/zend-expressive/pull/543) removes the
   class `Zend\Expressive\Middleware\RouteMiddleware`. Use the
   `PathBasedRoutingMiddleware` or `RouteMiddleware` from zend-expressive-router