mm/oom_kill: Disable scary messages for normal usecases

As the oom-killer is allowed to run (in rare situations only!) when
CONFIG_HAVE_USERSPACE_LOW_MEMORY_KILLER=y, disable dumping the
system memory state when the oom-killer kills a task.

Change-Id: I26965c0c8588721f0908202c4a9d67d26af1d704
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>