refactor: remove broken anon mode feature

- delete the anon mode hook/store and stop wiring publish flows through alternate signers
  - strip the settings UI, avatar warning, reply indicators, and FAQ text that referenced the toggle
  - drop the anon mode translation keys via scripts/update-translations.js

public/translations/en/default.json

@@ -222,8 +222,6 @@
   "static_gif": "Static GIF",
   "animated_gif": "Animated GIF",
   "hide_avatars": "Hide avatars",
-  "anon_mode": "Anon mode",
-  "anon_mode_description": "Use a unique user ID for each thread you post in. These IDs cannot be traced back to your original account.",
   "pending": "Pending",
   "failed": "Failed",
   "add": "Add",
@@ -248,7 +246,6 @@
   "crypto_address_yours": "Crypto address belongs to this account.",
   "delete_wallet": "Delete Wallet",
   "loading_board": "Loading board",
-  "avatar_warning": "You can't post with an avatar while anon mode is turned on. You can turn it off in your Plebbit Account settings.",
   "last_bumped": "Last Bumped",
   "threads_without_images_tip": "Only display threads that link to embeddable media",
   "hide_gore_boards_tip": "Don't display threads from boards with the \"gore\" tag",