refactor: remove unused electron::api::App::FileIconCallback (#46513)

refactor: remove electron::api::App::FileIconCallback

last use removed in 2018 by 3f15f516

Co-authored-by: trop[bot] <37223003+trop[bot]@users.noreply.github.com>
Co-authored-by: Charles Kerr <charles@charleskerr.com>

shell/browser/api/electron_api_app.h

@@ -33,10 +33,6 @@ namespace base {
 class FilePath;
 }
 
-namespace gfx {
-class Image;
-}
-
 namespace gin {
 template <typename T>
 class Handle;
@@ -64,9 +60,6 @@ class App final : public ElectronBrowserClient::Delegate,
                   private content::GpuDataManagerObserver,
                   private content::BrowserChildProcessObserver {
  public:
-  using FileIconCallback =
-      base::RepeatingCallback<void(v8::Local<v8::Value>, const gfx::Image&)>;
-
   static gin::Handle<App> Create(v8::Isolate* isolate);
   static App* Get();