fork: remove redundant TASK_UNINTERRUPTIBLE

TASK_KILLABLE already includes TASK_UNINTERRUPTIBLE, so there is no
need to add a separate TASK_UNINTERRUPTIBLE.

Link: https://lkml.kernel.org/r/20231208084115.1973285-1-haokexin@gmail.com


Signed-off-by: Kevin Hao <haokexin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>