Remove DESKTOP_STARTUP_ID code

This was removed upstream in https://chromium-review.googlesource.com/c/chromium/src/+/6819616 and I confirmed with the author that it was an intentional change. Going to mirror upstream and remove it here too.

filenames.gni

@@ -23,7 +23,6 @@ filenames = {
 
   lib_sources_linux = [
     "shell/browser/browser_linux.cc",
-    "shell/browser/electron_browser_main_parts_linux.cc",
     "shell/browser/lib/power_observer_linux.cc",
     "shell/browser/lib/power_observer_linux.h",
     "shell/browser/linux/unity_service.cc",

shell/browser/electron_browser_main_parts.cc

@@ -210,7 +210,6 @@ int ElectronBrowserMainParts::PreEarlyInitialization() {
   HandleSIGCHLD();
 #endif
 #if BUILDFLAG(IS_LINUX)
-  SetDesktopStartupId();
   ui::OzonePlatform::PreEarlyInitialization();
 #endif
 #if BUILDFLAG(IS_MAC)

shell/browser/electron_browser_main_parts.h

@@ -124,10 +124,6 @@ class ElectronBrowserMainParts : public content::BrowserMainParts {
       const scoped_refptr<base::SingleThreadTaskRunner>& task_runner);
 #endif
 
-#if BUILDFLAG(IS_LINUX)
-  void SetDesktopStartupId();
-#endif
-
 #if BUILDFLAG(IS_MAC)
   void FreeAppDelegate();
   void RegisterURLHandler();

shell/browser/electron_browser_main_parts_linux.cc

@@ -1,23 +0,0 @@
-// Copyright (c) 2022 GitHub, Inc.
-// Use of this source code is governed by the MIT license that can be
-// found in the LICENSE file.
-
-#include "shell/browser/electron_browser_main_parts.h"
-
-#include "base/command_line.h"
-#include "base/environment.h"
-
-namespace electron {
-
-void ElectronBrowserMainParts::SetDesktopStartupId() {
-  // TODO(clavin): this was removed upstream in
-  // https://chromium-review.googlesource.com/c/chromium/src/+/6819616 but it's
-  // not clear if that was intentional.
-  auto const env = base::Environment::Create();
-  auto* const command_line = base::CommandLine::ForCurrentProcess();
-  if (std::optional<std::string> desktop_startup_id =
-          env->GetVar("DESKTOP_STARTUP_ID"))
-    command_line->AppendSwitchASCII("desktop-startup-id", *desktop_startup_id);
-}
-
-}  // namespace electron