Remove default SSL cipher suite

If no "options.cryptoCredentialsDefaults.ciphers" option is set in the configuration, then Tedious defaults to the "RC4-MD5" cipher suite.

This is a very old cipher suite, and worse yet it uses MD5 which is disabled by many modern web servers and firewalls.

Rather than hard-code a default, I think that Tedious should not try to override the default cipher suite, but instead let the implementation choose one as part of normal TLS/SSL negotiation. That way, as cipher suites evolve, Tedious won't need to be updated again.

I see MD5 used elsewhere with HMAC, but I presume that's part of NTLM authentication and that it can't be replaced.