Merge pull request #6370 from OlegHahm/crypto_remove_twofish_rc5

sys/crypto/doc.txt

sys/crypto/rc5.c

sys/crypto/twofish.c

sys/include/crypto/ciphers.h

sys/include/crypto/rc5.h

sys/include/crypto/twofish.h

tests/unittests/tests-crypto/tests-crypto-twofish.c

tests/unittests/tests-crypto/tests-crypto.c

tests/unittests/tests-crypto/tests-crypto.h