opal/cmd_line: fix compiler warning

We don't use the "non-null" arg attribute stuff anywhere else, and we
don't use it on master.  So go ahead and remove it here, thereby
fixing a compiler warning (that we are redundantly checking the args
for NULL in the definition of the routine).

Signed-off-by: Jeff Squyres <[email protected]>

Author: jsquyres

opal/util/cmd_line.h

@@ -9,7 +9,7 @@
  *                         University of Stuttgart.  All rights reserved.
  * Copyright (c) 2004-2005 The Regents of the University of California.
  *                         All rights reserved.
- * Copyright (c) 2012 Cisco Systems, Inc.  All rights reserved.
+ * Copyright (c) 2012-2017 Cisco Systems, Inc.  All rights reserved
  * $COPYRIGHT$
  *
  * Additional copyrights may follow
@@ -566,7 +566,7 @@ BEGIN_C_DECLS
      * to opal_argv_free()) by the caller.
      */
     OPAL_DECLSPEC int opal_cmd_line_get_tail(opal_cmd_line_t *cmd, int *tailc,
-                                             char ***tailv) __opal_attribute_nonnull__(1) __opal_attribute_nonnull__(2);
+                                             char ***tailv);
 
 END_C_DECLS