NOMMU: Remove an extraneous no_printk()

Remove an extraneous no_printk() in mm/nommu.c that got missed when the
function got generalised from several things that used it in commit
12fdff3f

 ("Add a dummy printk function for the maintenance of unused
printks").

Without this, the following error is observed:

  mm/nommu.c:41: error: conflicting types for 'no_printk'
  include/linux/kernel.h:314: error: previous definition of 'no_printk' was here

Reported-by: Michal Simek <monstr@monstr.eu>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>