pid: pid_ns_ctl_handler: remove useless comment

commit 95846ecf("pid: replace pid bitmap implementation with IDR API")
removes 'last_pid' element, and use the idr_get_cursor-idr_set_cursor pair
to set the value of idr, so useless comments should be removed.

Link: https://lkml.kernel.org/r/tencent_157A2A1CAF19A3F5885F0687426159A19708@qq.comSigned-off-by: Rong Tao <rongtao@cestc.cn>
Cc: Aleksa Sarai <cyphar@cyphar.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Frederic Weisbecker <frederic@kernel.org>
Cc: Jeff Xu <jeffxu@google.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

kernel/pid_namespace.c

@@ -286,12 +286,6 @@ static int pid_ns_ctl_handler(struct ctl_table *table, int write,
 	if (write && !checkpoint_restore_ns_capable(pid_ns->user_ns))
 		return -EPERM;
 
-	/*
-	 * Writing directly to ns' last_pid field is OK, since this field
-	 * is volatile in a living namespace anyway and a code writing to
-	 * it should synchronize its usage with external means.
-	 */
-
 	next = idr_get_cursor(&pid_ns->idr) - 1;
 
 	tmp.data = &next;