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/EventLoop.cpp

@@ -23,9 +23,7 @@ EventLoop::EventLoop()
 {
 }
 
-EventLoop::~EventLoop()
-{
-}
+EventLoop::~EventLoop() = default;
 
 void EventLoop::schedule()
 {