[codex] Remove remote thread store implementation (#21596)

Remove the remote thread-store backend and checked-in protobuf
artifacts. We've moved these into another crate that link against this
one.

Also remove the config settings for thread store backend selection,
since we'll instead pass an instantiated thread store into the core-api
crate's main entrypoint.

codex-rs/config/src/config_toml.rs

@@ -345,14 +345,15 @@ pub struct ConfigToml {
     /// active.
     pub experimental_realtime_start_instructions: Option<String>,
 
-    /// Experimental / do not use. When set, app-server uses a remote thread
-    /// store at this endpoint instead of the local filesystem/SQLite store.
-    pub experimental_thread_store_endpoint: Option<String>,
-
     /// Experimental / do not use. When set, app-server fetches thread-scoped
     /// config from a remote service at this endpoint.
     pub experimental_thread_config_endpoint: Option<String>,
 
+    /// Removed. Former remote thread-store endpoint setting kept only so we can
+    /// fail fast instead of silently falling back to local persistence.
+    #[schemars(skip)]
+    pub experimental_thread_store_endpoint: Option<String>,
+
     /// Experimental / do not use. Selects the thread store implementation.
     pub experimental_thread_store: Option<ThreadStoreToml>,
     pub projects: Option<HashMap<String, ProjectConfig>>,
@@ -488,9 +489,6 @@ pub struct DebugConfigLockToml {
 #[serde(tag = "type", rename_all = "snake_case")]
 pub enum ThreadStoreToml {
     Local {},
-    Remote {
-        endpoint: String,
-    },
     #[schemars(skip)]
     InMemory {
         id: String,