Mark correct variables unused in FFI botan_{pub,priv}key_load_elgamal
Mark correct variables unused in FFI botan_{pub,priv}key_load_elgamal

Closes #1011

Rohde-Schwarz-Cybersecurity/botan,randombit/botan,Rohde-Schwarz-Cybersecurity/botan,webmaster128/botan,randombit/botan,Rohde-Schwarz-Cybersecurity/botan,Rohde-Schwarz-Cybersecurity/botan,webmaster128/botan,randombit/botan,randombit/botan,webmaster128/botan,webmaster128/botan,randombit/botan,webmaster128/botan,Rohde-Schwarz-Cybersecurity/botan,Rohde-Schwarz-Cybersecurity/botan