compute tip scale when loading from brush tips, remove tip_width which was replaced by tip_scale

src/node_panel_brush.h

@@ -105,7 +105,6 @@ class NodePanelBrushPreset : public Node
 
         glm::vec4 m_tip_color{ 0, 0, 0, 1 };
         glm::vec2 m_tip_scale = { 1.f, 1.f };
-        float m_tip_width = 1.f;
         float m_tip_size = 0;
         float m_tip_spacing = 0;
         float m_tip_flow = 0;