Revert "Clear a cached user in RequestGuard if a request is changed (#35692)"

This reverts commit 0d601f5.

Author: taylorotwell

src/Illuminate/Auth/RequestGuard.php

@@ -82,8 +82,6 @@ public function setRequest(Request $request)
     {
         $this->request = $request;
 
-        $this->user = null;
-
         return $this;
     }
 }