oom: remove constraint argument from select_bad_process and __out_of_memory

select_bad_process() and __out_of_memory() doe not need their enum
oom_constraint arguments: it's possible to pass a NULL nodemask if
constraint == CONSTRAINT_MEMORY_POLICY in the caller, out_of_memory().

Signed-off-by: David Rientjes <rientjes@google.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>