Drop debug-client prompt state tracking (#25070)

Deletes `codex-rs/debug-client/src/state.rs` as one step in removing the
stale app-server debug client.

This intentionally leaves Cargo workspace and lockfile cleanup for a
later follow-up PR.

codex-rs/debug-client/src/state.rs

@@ -1,28 +0,0 @@
-use std::collections::HashMap;
-
-use codex_app_server_protocol::RequestId;
-
-#[derive(Debug, Default)]
-pub struct State {
-    pub pending: HashMap<RequestId, PendingRequest>,
-    pub thread_id: Option<String>,
-    pub known_threads: Vec<String>,
-}
-
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
-pub enum PendingRequest {
-    Start,
-    Resume,
-    List,
-}
-
-#[derive(Debug, Clone)]
-pub enum ReaderEvent {
-    ThreadReady {
-        thread_id: String,
-    },
-    ThreadList {
-        thread_ids: Vec<String>,
-        next_cursor: Option<String>,
-    },
-}