PHP: Removed previously failing tests from the failure list.

conformance/failure_list_php_c.txt

@@ -1,4 +1,2 @@
 Recommended.Proto2.JsonInput.FieldNameExtension.Validator
-Recommended.Proto3.JsonInput.NullValueInOtherOneofNewFormat.Validator
-Recommended.Proto3.JsonInput.NullValueInOtherOneofOldFormat.Validator
 Required.Proto2.JsonInput.StoresDefaultPrimitive.Validator