openssl: Remove deprecated functions from des_encrypt()

openssl: Remove deprecated functions from des_encrypt()

NetworkManager-CI detected systematic failures on test scenarios using
MSCHAPv2 when wpa_supplicant uses OpenSSL-3.0.0.
The 'test_module_tests.py' script also fails, and the following log is
shown:

 1627404013.761569: generate_nt_response failed
 1627404013.761582: ms_funcs: 1 error

It seems that either DES_set_key() or DES_ecb_encrypt() changed their
semantic, but it doesn't make sense to fix them since their use has been
deprecated. Converting des_encrypt() to avoid use of deprecated
functions proved to fix the problem, and removed a couple of build
warnings at the same time.

Reported-by: Vladimir Benes <vbenes@redhat.com>
Signed-off-by: Davide Caratti <davide.caratti@gmail.com>