Revert mistake made in merge

When merging master -> 3.next I made a mistake and chose the wrong side
of the conflict. This restores changes made in #12561, and removes
changes made in #12748

src/Routing/Middleware/RoutingMiddleware.php

@@ -17,7 +17,6 @@ namespace Cake\Routing\Middleware;
 use Cake\Cache\Cache;
 use Cake\Core\HttpApplicationInterface;
 use Cake\Core\PluginApplicationInterface;
-use Cake\Http\BaseApplication;
 use Cake\Http\MiddlewareQueue;
 use Cake\Http\Runner;
 use Cake\Routing\Exception\RedirectException;
@@ -40,7 +39,7 @@ class RoutingMiddleware
     /**
      * The application that will have its routing hook invoked.
      *
-     * @var \Cake\Http\BaseApplication|null
+     * @var \Cake\Core\HttpApplicationInterface|null
      */
     protected $app;
 
@@ -55,10 +54,10 @@ class RoutingMiddleware
     /**
      * Constructor
      *
-     * @param \Cake\Http\BaseApplication|null $app The application instance that routes are defined on.
+     * @param \Cake\Core\HttpApplicationInterface|null $app The application instance that routes are defined on.
      * @param string|null $cacheConfig The cache config name to use or null to disable routes cache
      */
-    public function __construct(BaseApplication $app = null, $cacheConfig = null)
+    public function __construct(HttpApplicationInterface $app = null, $cacheConfig = null)
     {
         $this->app = $app;
         $this->cacheConfig = $cacheConfig;