ssl_server2 had a check that we never try to use a minor version lower
than 2 with DTLS, but that check is no longer needed, as there's no way
that would happen now that MBEDTLS_SSL_MINOR_VERSION_1 is no longer
public.
Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>