remove png function as it was not very useful

src/Painter.cpp

@@ -102,11 +102,4 @@ void Painter::flush_paint_group() {
     m_cairo->get_target()->flush();
 }
 
-Point Painter::png(std::string path) {
-    auto image = Cairo::ImageSurface::create_from_png(path.c_str());
-    m_cairo->set_source(image, 0, 0);
-
-    return Point(image->get_width(), image->get_height());
-}
-
 }

src/Painter.hpp

@@ -30,7 +30,6 @@ public:
     bool can_paint() { if (m_cairo) return true; else return false; }
 
     void source_rgb(RGB source_rgb);
-    Point png(std::string path);
     void fill();
 
     void begin_paint_group();