remove unused using

Signed-off-by: Rosen Penev <rosenp@gmail.com>

src/webpimage.cpp

@@ -69,7 +69,6 @@ namespace {
 // *****************************************************************************
 // class member definitions
 namespace Exiv2 {
-using namespace Exiv2::Internal;
 
 WebPImage::WebPImage(BasicIo::UniquePtr io) : Image(ImageType::webp, mdNone, std::move(io)) {
 }  // WebPImage::WebPImage