Libraries: Use default constructors/destructors in LibJS

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/LibJS/SyntaxHighlighter.cpp

@@ -124,9 +124,4 @@ bool SyntaxHighlighter::token_types_equal(u64 token1, u64 token2) const
 {
     return static_cast<JS::TokenType>(token1) == static_cast<JS::TokenType>(token2);
 }
-
-SyntaxHighlighter::~SyntaxHighlighter()
-{
-}
-
 }