Libraries: Use default constructors/destructors in LibCrypto

https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#cother-other-default-operation-rules

"The compiler is more likely to get the default semantics right and
you cannot implement these functions better than the compiler."

Userland/Libraries/LibCrypto/BigInt/UnsignedBigInteger.h

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
+ * Copyright (c) 2022, the SerenityOS developers.
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -31,7 +32,7 @@ public:
 
     explicit UnsignedBigInteger(const u8* ptr, size_t length);
 
-    UnsignedBigInteger() { }
+    UnsignedBigInteger() = default;
 
     static UnsignedBigInteger create_invalid();