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/MessageChannel.cpp

@@ -22,8 +22,6 @@ MessageChannel::MessageChannel()
     m_port1->entangle_with(*m_port2);
 }
 
-MessageChannel::~MessageChannel()
-{
-}
+MessageChannel::~MessageChannel() = default;
 
 }