include/asm-generic/topology.h: remove unused parent_node() macro

Commit a7be6e5a7f8d ("mm: drop useless local parameters of
__register_one_node()") removed the last user of parent_node().

The parent_node() macro in generic situation is unnecessary.

Remove it for cleanup.

Link: http://lkml.kernel.org/r/1504234599-29533-8-git-send-email-douly.fnst@cn.fujitsu.com
Signed-off-by: Dou Liyang <douly.fnst@cn.fujitsu.com>
Reported-by: Michael Ellerman <mpe@ellerman.id.au>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/asm-generic/topology.h

@@ -44,9 +44,6 @@
 #define cpu_to_mem(cpu)		((void)(cpu),0)
 #endif
 
-#ifndef parent_node
-#define parent_node(node)	((void)(node),0)
-#endif
 #ifndef cpumask_of_node
   #ifdef CONFIG_NEED_MULTIPLE_NODES
     #define cpumask_of_node(node)	((node) == 0 ? cpu_online_mask : cpu_none_mask)