[POWERPC] Remove redundant display of free swap space in show_mem()

show_mem() has no need to print the amount of free swap space manually
because show_free_areas() does this already and is called by the
former.

The two outputs only differ in text formatting:

  printk("Free swap  = %lukB\n", ...);
  printk("Free swap:       %6ldkB\n", ...);

Signed-off-by: Johannes Weiner <hannes@saeurebad.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>