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/JPGLoader.cpp

@@ -1232,9 +1232,7 @@ JPGImageDecoderPlugin::JPGImageDecoderPlugin(const u8* data, size_t size)
     m_context->huffman_stream.stream.ensure_capacity(50 * KiB);
 }
 
-JPGImageDecoderPlugin::~JPGImageDecoderPlugin()
-{
-}
+JPGImageDecoderPlugin::~JPGImageDecoderPlugin() = default;
 
 IntSize JPGImageDecoderPlugin::size()
 {