Relax isPrivate checks in the encrypt/decrypt methods

The master index uses RSA signatures in some builds. As such, we need to
be able to encrypt with a private key and decrypt with a public key.

Signed-off-by: Graham <gpe@openrs2.org>

crypto/src/main/kotlin/org/openrs2/crypto/Rsa.kt

@@ -88,7 +88,6 @@ public object Rsa {
     }
 
     public fun encrypt(plaintext: BigInteger, key: RSAKeyParameters): BigInteger {
-        require(!key.isPrivate)
         return plaintext.modPow(key.exponent, key.modulus)
     }
 
@@ -107,8 +106,6 @@ public object Rsa {
     }
 
     public fun decrypt(ciphertext: BigInteger, key: RSAKeyParameters): BigInteger {
-        require(key.isPrivate)
-
         if (key is RSAPrivateCrtKeyParameters) {
             // blind the input
             val e = key.publicExponent