Remove some unused theming code for GTK.

ui/views/linux_ui/linux_ui.h

Index: ui/views/linux_ui/linux_ui.h
diff --git a/ui/views/linux_ui/linux_ui.h b/ui/views/linux_ui/linux_ui.h
index 86a3d5a1bb074f0159c98b9173606bac9d7d7363..bbbaf572b72941298cd16972d9e862dcb3495f13 100644
--- a/ui/views/linux_ui/linux_ui.h
+++ b/ui/views/linux_ui/linux_ui.h
@@ -84,11 +84,8 @@ class VIEWS_EXPORT LinuxUI : public ui::LinuxInputMethodContextFactory,
   // unconditionally.
   virtual void MaterialDesignControllerReady() = 0;
 
-  // Returns a themed image per theme_provider.h
-  virtual gfx::Image GetThemeImageNamed(int id) const = 0;
   virtual bool GetTint(int id, color_utils::HSL* tint) const = 0;
   virtual bool GetColor(int id, SkColor* color) const = 0;
-  virtual bool HasCustomImage(int id) const = 0;
 
   // Returns the preferences that we pass to WebKit.
   virtual SkColor GetFocusRingColor() const = 0;