crypto: aegis - Cleanup license mess

Precise and non-ambiguous license information is important. The recently
added aegis header file has a SPDX license identifier, which is nice, but
at the same time it has a contradictionary license boiler plate text.

  SPDX-License-Identifier: GPL-2.0

versus

  * This program is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License as published by the Free
  * Software Foundation; either version 2 of the License, or (at your option)
  * any later version

Oh well.

As the other aegis related files are licensed under the GPL v2 or later,
it's assumed that the boiler plate code is correct, but the SPDX license
identifier is wrong.

Fix the SPDX identifier and remove the boiler plate as it is redundant.

Fixes: f606a88e ("crypto: aegis - Add generic AEGIS AEAD implementations")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Ondrej Mosnacek <omosnacek@gmail.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: linux-crypto@vger.kernel.org
Acked-by: Ondrej Mosnacek <omosnacek@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>