Remove useless assertion

Author: alcaeus

src/ChangeStream.php

@@ -18,7 +18,6 @@
 namespace MongoDB;
 
 use Iterator;
-use MongoDB\BSON\Document;
 use MongoDB\Codec\DocumentCodec;
 use MongoDB\Driver\CursorId;
 use MongoDB\Driver\Exception\ConnectionException;
@@ -29,7 +28,6 @@
 use MongoDB\Model\ChangeStreamIterator;
 use ReturnTypeWillChange;
 
-use function assert;
 use function call_user_func;
 use function in_array;
 
@@ -116,8 +114,6 @@ public function current()
             return $value;
         }
 
-        assert($value === null || $value instanceof Document);
-
         return $this->codec->decodeIfSupported($value);
     }