imgui-util: Fix compilation if imgui version has docking

debugging/glow-extras/debugging/imgui-util.cc

@@ -133,7 +133,6 @@ void glow::debugging::applyGlowImguiTheme(bool darkMode)
     style.GrabRounding = 3;
 
 #ifdef IMGUI_HAS_DOCK
-    style.TabBorderSize = is3D;
     style.TabRounding = 3;
 
     colors[ImGuiCol_DockingEmptyBg] = ImVec4(0.38f, 0.38f, 0.38f, 1.00f);