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/DDSLoader.cpp

@@ -944,9 +944,7 @@ DDSImageDecoderPlugin::DDSImageDecoderPlugin(const u8* data, size_t size)
     m_context->data_size = size;
 }
 
-DDSImageDecoderPlugin::~DDSImageDecoderPlugin()
-{
-}
+DDSImageDecoderPlugin::~DDSImageDecoderPlugin() = default;
 
 IntSize DDSImageDecoderPlugin::size()
 {