mm/kfence: remove hung_task cruft

mm/kfence: remove hung_task cruft

commit fdf756f71271 ("sched: Fix more TASK_state comparisons") makes
hung_task not to monitor TASK_IDLE tasks.  The special handling to
workaround hung_task warnings is not required anymore.

Link: https://lkml.kernel.org/r/1667986006-25420-1-git-send-email-quic_pkondeti@quicinc.com
Signed-off-by: Pavankumar Kondeti <quic_pkondeti@quicinc.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>