remove opts param from signature

src/php/tests/generated_code/GeneratedCodeWithCallbackTest.php

@@ -38,7 +38,6 @@ class GeneratedCodeWithCallbackTest extends AbstractGeneratedCodeTest {
     self::$client = new math\MathClient(new Grpc\BaseStub(
         getenv('GRPC_TEST_HOST'), ['update_metadata' =>
                                    function($a_hash,
-                                            $opts = array(),
                                             $client = array()) {
                                      $a_copy = $a_hash;
                                      $a_copy['foo'] = ['bar'];