proc: array: drop stale FIXME about RCU in task_sig()

proc: array: drop stale FIXME about RCU in task_sig()

task_sig() already wraps the SigQ rlimit read in an explicit RCU read-side
critical section.  Drop the stale FIXME comment and keep using
task_ucounts() for the ucounts access.

No functional change.

Link: https://lkml.kernel.org/r/20260215124511.14227-1-jaime.saguillo@gmail.com
Signed-off-by: Jaime Saguillo Revilla <jaime.saguillo@gmail.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Cc: Christian Brauner <brauner@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>