Revert "main.c: use EVP_??cryptInit instead of EVP_??cryptInit_ex"

This reverts commit baa09fcdff3c566ae1554fc0c922909f6daee3b0.

Because http://www.openssl.org/docs/crypto/EVP_EncryptInit.html says:
The functions EVP_EncryptInit(), EVP_EncryptFinal(), EVP_DecryptInit(), EVP_CipherInit() and EVP_CipherFinal() are obsolete but are retained for compatibility with existing code. New code should use EVP_EncryptInit_ex(), EVP_EncryptFinal_ex(), EVP_DecryptInit_ex(), EVP_DecryptFinal_ex(), EVP_CipherInit_ex() and EVP_CipherFinal_ex() because they can reuse an existing context without allocating and freeing it up on each call.