LibCrypto: Exclude class_name() methods from the Kernel

These are only used by Userland and contain infallible String
allocations, so let's just ifdef them out of the Kernel.

Userland/Libraries/LibCrypto/Hash/HashFunction.h

@@ -51,7 +51,9 @@ public:
 
     virtual void reset() = 0;
 
+#ifndef KERNEL
     virtual String class_name() const = 0;
+#endif
 
 protected:
     virtual ~HashFunction() = default;