package/dropbear: bump to version 2020.80

package/dropbear: bump to version 2020.80

remove merged patches.

LICENSE diff:
- Copyright (c) 2002-2015 Matt Johnston
+ Copyright (c) 2002-2020 Matt Johnston
- LibTomCrypt and LibTomMath are written by Tom St Denis, and are Public Domain.
+ LibTomCrypt and LibTomMath are written by Tom St Denis and others, see
+ libtomcrypt/LICENSE and libtommath/LICENSE.

Signed-off-by: Francois Perrad <francois.perrad@gadz.org>
Acked-by: Alexander Dahl <post@lespocky.de>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>