f examples/gcoap: remove tweetnacl
f examples/gcoap: remove tweetnacl

jbeyerstedt/RIOT-OTA-update,jbeyerstedt/RIOT-OTA-update,jbeyerstedt/RIOT-OTA-update,jbeyerstedt/RIOT-OTA-update,jbeyerstedt/RIOT-OTA-update