genirq: Remove license boilerplate/references

Now that SPDX identifiers are in place, remove the boilerplate or
references.

The change in timings.c has been acked by the author.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Philippe Ombredanne <pombredanne@nexb.com>
Link: https://lkml.kernel.org/r/20180314212030.668321222@linutronix.de
diff --git a/kernel/irq/debugfs.c b/kernel/irq/debugfs.c
index c8cc6ce..4dadeb3 100644
--- a/kernel/irq/debugfs.c
+++ b/kernel/irq/debugfs.c
@@ -1,9 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
-/*
- * Copyright 2017 Thomas Gleixner <tglx@linutronix.de>
- *
- * This file is licensed under the GPL V2.
- */
+// Copyright 2017 Thomas Gleixner <tglx@linutronix.de>
+
 #include <linux/irqdomain.h>
 #include <linux/irq.h>
 #include <linux/uaccess.h>