Drop _gcry_cipher_ofb_decrypt as it duplicates _gcry_cipher_ofb_encrypt

* cipher/cipher.c (cipher_decrypt): Use _gcry_cipher_ofb_encrypt for OFB
  decryption.
* cipher/cipher-internal.h: Remove _gcry_cipher_ofb_decrypt declaration.
* cipher/cipher-ofb.c (_gcry_cipher_ofb_decrypt): Remove.
  (_gcry_cipher_ofb_encrypt): remove copying of IV to lastiv, it's
  unused there.

Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Deduplicate code for ECB encryption and decryption

* cipher/cipher.c (do_ecb_crypt): New, based on old 'do_ecb_encrypt'.
(do_ecb_encrypt): Use 'do_ecb_crypt', pass encryption function.
(do_ecb_decrypt): Use 'do_ecb_crypt', pass decryption function.
--

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>