[BACKPORT] HID: apple: remove unused members from struct apple_sc_backlight

Commit f740106aedd3 (HID: apple: remove unused members from struct apple_sc_backlight) in Linus’ tree imo should be back ported to:

1. Linux 6.6 2. Linux 6.1

since there hasn't been any change to the backlight code in the driver ever since it has been upstreamed. So it should be safe to remove the unused members from struct apple_sc_backlight