refactor: remove unused fields, methods in gin_helper::Locker (#39803)

* refactor: remove unused field gin_helper::Locker::g_is_browser_process

refactor: remove unused field gin_helper::Locker::g_is_renderer_process

refactor: make field const gin_helper::Locker::locker_

* refactor: remove unused declaration gin_helper::Locker::new()

refactor: remove unused declaration gin_helper::Locker::delete()

* refactor: make field const electron::JavascriptEnvironment::locker_

* refactor: remove unused #include gin_helper/locker.h