Remove unimplemented methods from CryptoSquare class (#2465)

These methods are not required for tests to pass, and are not mentioned in the requirements.

Author: donbru

exercises/practice/crypto-square/CryptoSquare.cs

@@ -1,22 +1,7 @@
 public static class CryptoSquare
 {
-    public static string NormalizedPlaintext(string plaintext)
-    {
-        throw new NotImplementedException("You need to implement this method.");
-    }
-
-    public static IEnumerable<string> PlaintextSegments(string plaintext)
-    {
-        throw new NotImplementedException("You need to implement this method.");
-    }
-
-    public static string Encoded(string plaintext)
-    {
-        throw new NotImplementedException("You need to implement this method.");
-    }
-
     public static string Ciphertext(string plaintext)
     {
         throw new NotImplementedException("You need to implement this method.");
     }
-}
+}