proto: Remove unused UpdateUserSettings message (#20005)

Release Notes:

- N/A

crates/proto/src/proto.rs

@@ -342,7 +342,6 @@ messages!(
     (FindSearchCandidates, Background),
     (FindSearchCandidatesResponse, Background),
     (CloseBuffer, Foreground),
-    (UpdateUserSettings, Foreground),
     (ShutdownRemoteServer, Foreground),
     (RemoveWorktree, Foreground),
     (LanguageServerLog, Foreground),
@@ -559,7 +558,6 @@ entity_messages!(
     UpdateContext,
     SynchronizeContexts,
     LspExtSwitchSourceHeader,
-    UpdateUserSettings,
     LanguageServerLog,
     Toast,
     HideToast,