LibCrypto: Exclude AESCipher{Block, Key}::to_string() from the Kernel

These use infallible Strings and are not actually used in the Kernel,
so let's just ifdef them out for now.

Userland/Libraries/LibCrypto/Cipher/AES.cpp

@@ -24,6 +24,7 @@ constexpr void swap_keys(u32* keys, size_t i, size_t j)
     keys[j] = temp;
 }
 
+#ifndef KERNEL
 String AESCipherBlock::to_string() const
 {
     StringBuilder builder;
@@ -39,6 +40,7 @@ String AESCipherKey::to_string() const
         builder.appendff("{:02x}", m_rd_keys[i]);
     return builder.build();
 }
+#endif
 
 void AESCipherKey::expand_encrypt_key(ReadonlyBytes user_key, size_t bits)
 {

Userland/Libraries/LibCrypto/Cipher/AES.h

@@ -6,13 +6,16 @@
 
 #pragma once
 
-#include <AK/String.h>
 #include <AK/Vector.h>
 #include <LibCrypto/Cipher/Cipher.h>
 #include <LibCrypto/Cipher/Mode/CBC.h>
 #include <LibCrypto/Cipher/Mode/CTR.h>
 #include <LibCrypto/Cipher/Mode/GCM.h>
 
+#ifndef KERNEL
+#    include <AK/String.h>
+#endif
+
 namespace Crypto {
 namespace Cipher {
 
@@ -44,7 +47,9 @@ public:
             m_data[i] ^= ivec[i];
     }
 
+#ifndef KERNEL
     String to_string() const;
+#endif
 
 private:
     constexpr static size_t data_size() { return sizeof(m_data); }
@@ -57,7 +62,11 @@ struct AESCipherKey : public CipherKey {
     virtual void expand_encrypt_key(ReadonlyBytes user_key, size_t bits) override;
     virtual void expand_decrypt_key(ReadonlyBytes user_key, size_t bits) override;
     static bool is_valid_key_size(size_t bits) { return bits == 128 || bits == 192 || bits == 256; };
+
+#ifndef KERNEL
     String to_string() const;
+#endif
+
     const u32* round_keys() const
     {
         return (const u32*)m_rd_keys;