Libraries: Use default constructors/destructors in LibGfx

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/LibGfx/Painter.h

@@ -26,7 +26,7 @@ namespace Gfx {
 class Painter {
 public:
     explicit Painter(Gfx::Bitmap&);
-    ~Painter();
+    ~Painter() = default;
 
     enum class LineStyle {
         Solid,