Libraries: Use default constructors/destructors in LibWeb

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/LibWeb/HTML/EventLoop/Task.cpp

@@ -16,9 +16,7 @@ Task::Task(Source source, DOM::Document* document, Function<void()> steps)
 {
 }
 
-Task::~Task()
-{
-}
+Task::~Task() = default;
 
 void Task::execute()
 {