Address unused variable warnings

Polyhedron/demo/Polyhedron/Plugins/Mesh_3/Io_image_plugin.cpp

@@ -68,6 +68,7 @@
 #endif
 
 #include <CGAL/Three/Three.h>
+#include <CGAL/use.h>
 
 #include <boost/type_traits.hpp>
 #include <optional>
@@ -92,6 +93,8 @@ load_vtk_file(QFileInfo fileinfo, Image* image)
     *image = CGAL::IO::read_vtk_image_data(vtk_image); // copy the image data
     return true;
 #else
+    CGAL_USE(fileinfo);
+    CGAL_USE(image);
     return false;
 #endif
 }

Polyhedron/demo/Polyhedron/Plugins/Mesh_3/Mesh_3_plugin.cpp

@@ -50,9 +50,6 @@ auto make_not_null(T&& t) {
 
 using namespace CGAL::Three;
 
-// Constants
-const QColor default_mesh_color(45,169,70);
-
 #include "Mesh_3_plugin_cgal_code.h" // declare functions `cgal_code_mesh_3`
 #include "split_polylines.h"
 #include <CGAL/Mesh_facet_topology.h>