driver/base/node: remove unnecessary kfree of node struct from unregister_one_node

Commit 92d585ef ("numa: fix NULL pointer access and memory
leak in unregister_one_node()") added kfree() of node struct in
unregister_one_node(). But node struct is freed by node_device_release()
which is called in  unregister_node(). So by adding the kfree(),
node struct is freed two times.

While hot removing memory, the commit leads the following BUG_ON():

  kernel BUG at mm/slub.c:3346!
  invalid opcode: 0000 [#1] SMP
  [...]
  Call Trace:
   [...] unregister_one_node
   [...] try_offline_node
   [...] remove_memory
   [...] acpi_memory_device_remove
   [...] acpi_bus_trim
   [...] acpi_bus_trim
   [...] acpi_device_hotplug
   [...] acpi_hotplug_work_fn
   [...] process_one_work
   [...] worker_thread
   [...] ? rescuer_thread
   [...] kthread
   [...] ? kthread_create_on_node
   [...] ret_from_fork
   [...] ? kthread_create_on_node

This patch removes unnecessary kfree() from unregister_one_node().

Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Cc: Xishi Qiu <qiuxishi@huawei.com>
Cc: stable@vger.kernel.org # v3.16+
Fixes: 92d585ef "numa: fix NULL pointer access and memory leak in unregister_one_node()"
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>