x86/topology: Remove the unused parent_node() macro

Commit:

  a7be6e5a ("mm: drop useless local parameters of __register_one_node()")

... removed the last user of parent_node(), so remove the macro.
Reported-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Dou Liyang <douly.fnst@cn.fujitsu.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1501076076-1974-11-git-send-email-douly.fnst@cn.fujitsu.comSigned-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/include/asm/topology.h

@@ -75,12 +75,6 @@ static inline const struct cpumask *cpumask_of_node(int node)
 
 extern void setup_node_to_cpumask_map(void);
 
-/*
- * Returns the number of the node containing Node 'node'. This
- * architecture is flat, so it is a pretty simple function!
- */
-#define parent_node(node) (node)
-
 #define pcibus_to_node(bus) __pcibus_to_node(bus)
 
 extern int __node_distance(int, int);