powerpc/topology: Remove the unused parent_node() macro

Commit a7be6e5a ("mm: drop useless local parameters of
__register_one_node()") removes the last user of parent_node().

The parent_node() macro in POWERPC platform is unnecessary.

Remove it for cleanup.
Reported-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Dou Liyang <douly.fnst@cn.fujitsu.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/topology.h

@@ -16,8 +16,6 @@ struct device_node;
 
 #include <asm/mmzone.h>
 
-#define parent_node(node)	(node)
-
 #define cpumask_of_node(node) ((node) == -1 ?				\
 			       cpu_all_mask :				\
 			       node_to_cpumask_map[node])