Don't assert against changing validate response

keyPerIndex was changed in 4.2, so we may no longer assert against it

tests/Alcaeus/MongoDbAdapter/Mongo/MongoCollectionTest.php

@@ -1896,7 +1896,6 @@ class MongoCollectionTest extends TestCase
                 'ns' => 'mongo-php-adapter.test',
                 'nrecords' => 1,
                 'nIndexes' => 1,
-                'keysPerIndex' => ['mongo-php-adapter.test.$_id_' => 1],
                 'valid' => true,
                 'errors' => [],
             ],