RSADispose special handling can be removed

[mregen]

Type of Issue
[ ] Bug [X ] Enhancement [ ] Compliance [ ] Question [ ] Help wanted

There is a lot of special handling for Mono and RSA keys, the issue is fixed since a long time and should be removed:
mono/mono#6306
search for RSADispose()

Code snippets

        internal static RsaPrivateCrtKeyParameters GetPrivateKeyParameter(X509Certificate2 certificate)
        {
            RSA rsa = null;
            try
            {
                // try to get signing/private key from certificate passed in
                rsa = certificate.GetRSAPrivateKey();
                return GetPrivateKeyParameter(rsa);
            }
            finally
            {
                RsaUtils.RSADispose(rsa);
            }
        }

Environment (please complete the following information):

• Runtime: [Mono]

[mregen]

test