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/CanvasGradient.cpp

@@ -43,9 +43,7 @@ CanvasGradient::CanvasGradient(Type type)
 {
 }
 
-CanvasGradient::~CanvasGradient()
-{
-}
+CanvasGradient::~CanvasGradient() = default;
 
 // https://html.spec.whatwg.org/multipage/canvas.html#dom-canvasgradient-addcolorstop
 DOM::ExceptionOr<void> CanvasGradient::add_color_stop(double offset, String const& color)