Adjust an outdated comment.

os_sync_free(), which hid resource leaks, was removed in MySQL 5.7.

storage/innobase/include/sync0debug.h

 /*****************************************************************************
 
 Copyright (c) 2013, 2015, Oracle and/or its affiliates. All Rights Reserved.
+Copyright (c) 2017, MariaDB Corporation. All Rights Reserved.
 
 Portions of this file contain modifications contributed and copyrighted by
 Google, Inc. Those modifications are gratefully acknowledged and are described
@@ -39,7 +40,7 @@ Created 2012-08-21 Sunny Bains
 void
 sync_check_init();
 
-/** Frees the resources in synchronization data structures. */
+/** Free the InnoDB synchronization data structures. */
 void
 sync_check_close();
 

storage/innobase/sync/sync0debug.cc

 /*****************************************************************************
 
 Copyright (c) 2014, 2016, Oracle and/or its affiliates. All Rights Reserved.
+Copyright (c) 2017, MariaDB Corporation. All Rights Reserved.
 
 Portions of this file contain modifications contributed and copyrighted by
 Google, Inc. Those modifications are gratefully acknowledged and are described
@@ -1787,8 +1788,7 @@ sync_check_init()
 	sync_array_init(OS_THREAD_MAX_N);
 }
 
-/** Frees the resources in InnoDB's own synchronization data structures. Use
-os_sync_free() after calling this. */
+/** Free the InnoDB synchronization data structures. */
 void
 sync_check_close()
 {