emb6: deprecate package
emb6: deprecate package

I basically didn't work on `emb6` since 2016 and adapting to the newest
version would mean some major overhaul. However, the development at
their end seems to be stalled [since March 2018][emb6-develop] as well.
All this speaks for deprecating this package.

[emb6-develop]: https://github.com/hso-esk/emb6/tree/develop

josephnoir/RIOT,OlegHahm/RIOT,RIOT-OS/RIOT,ant9000/RIOT,smlng/RIOT,toonst/RIOT,smlng/RIOT,kYc0o/RIOT,OTAkeys/RIOT,basilfx/RIOT,x3ro/RIOT,ant9000/RIOT,aeneby/RIOT,basilfx/RIOT,toonst/RIOT,toonst/RIOT,yogo1212/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,basilfx/RIOT,kaspar030/RIOT,mtausig/RIOT,miri64/RIOT,yogo1212/RIOT,miri64/RIOT,basilfx/RIOT,authmillenon/RIOT,yogo1212/RIOT,jasonatran/RIOT,kaspar030/RIOT,authmillenon/RIOT,OlegHahm/RIOT,yogo1212/RIOT,kYc0o/RIOT,ant9000/RIOT,x3ro/RIOT,kYc0o/RIOT,aeneby/RIOT,x3ro/RIOT,josephnoir/RIOT,josephnoir/RIOT,jasonatran/RIOT,mtausig/RIOT,mtausig/RIOT,OlegHahm/RIOT,aeneby/RIOT,authmillenon/RIOT,toonst/RIOT,josephnoir/RIOT,jasonatran/RIOT,authmillenon/RIOT,smlng/RIOT,josephnoir/RIOT,miri64/RIOT,smlng/RIOT,aeneby/RIOT,x3ro/RIOT,OTAkeys/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,basilfx/RIOT,kaspar030/RIOT,OTAkeys/RIOT,OTAkeys/RIOT,yogo1212/RIOT,OTAkeys/RIOT,miri64/RIOT,jasonatran/RIOT,kYc0o/RIOT,authmillenon/RIOT,aeneby/RIOT,smlng/RIOT,mtausig/RIOT,miri64/RIOT,x3ro/RIOT,toonst/RIOT,yogo1212/RIOT,ant9000/RIOT,mtausig/RIOT,ant9000/RIOT,kaspar030/RIOT,kYc0o/RIOT,kaspar030/RIOT,OlegHahm/RIOT,RIOT-OS/RIOT,RIOT-OS/RIOT