Remove several unused members from AchievementManager. These became unused in https://github.com/dolphin-emu/dolphin/pull/12639 which switched from the rcheevos rc_runtime interface to rc_client.
Remove several unused members from AchievementManager. These became unused in https://github.com/dolphin-emu/dolphin/pull/12639 which switched from the rcheevos rc_runtime interface to rc_client.