seccomp_user_notif.2: Remove FIXME asking about usefulness of POLLOUT/EPOLLOT

According to Tycho Andersen, he had no particular use case
in mind when building this detail into tha API.

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
diff --git a/man2/seccomp_user_notif.2 b/man2/seccomp_user_notif.2
index f3f7292..e5e4d1e 100644
--- a/man2/seccomp_user_notif.2
+++ b/man2/seccomp_user_notif.2
@@ -669,8 +669,6 @@
 .B SECCOMP_IOCTL_NOTIF_SEND
 .BR ioctl (2)
 operation.
-.\" FIXME
-.\" But (how) is the writable/(E)POLLOUT useful?
 .IP \(bu
 After the last thread using the filter has terminated and been reaped using
 .BR waitpid (2)