Remove hand-written CipherMode

Author: scott-xu

README.md

@@ -123,7 +123,6 @@ The main types provided by this library are:
 
 Private keys in OpenSSL traditional PEM format can be encrypted using one of the following cipher methods:
 * DES-EDE3-CBC
-* DES-EDE3-CFB
 * AES-128-CBC
 * AES-192-CBC
 * AES-256-CBC

src/Renci.SshNet/PrivateKeyFile.PKCS1.cs

@@ -53,9 +53,6 @@ public Key Parse()
                         case "DES-EDE3-CBC":
                             cipher = new CipherInfo(192, (key, iv) => new TripleDesCipher(key, iv, CipherMode.CBC, pkcs7Padding: true));
                             break;
-                        case "DES-EDE3-CFB":
-                            cipher = new CipherInfo(192, (key, iv) => new TripleDesCipher(key, iv, CipherMode.CFB, pkcs7Padding: false));
-                            break;
                         case "AES-128-CBC":
                             cipher = new CipherInfo(128, (key, iv) => new AesCipher(key, iv, CipherMode.CBC, pkcs7Padding: true));
                             break;

src/Renci.SshNet/PrivateKeyFile.cs

@@ -45,9 +45,6 @@ namespace Renci.SshNet
     ///         <description>DES-EDE3-CBC</description>
     ///     </item>
     ///     <item>
-    ///         <description>DES-EDE3-CFB</description>
-    ///     </item>
-    ///     <item>
     ///         <description>AES-128-CBC</description>
     ///     </item>
     ///     <item>