Drop the stale debug-client manifest (#25063)

Deletes `codex-rs/debug-client/Cargo.toml` 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/Cargo.toml

@@ -1,18 +0,0 @@
-[package]
-name = "codex-debug-client"
-version.workspace = true
-edition.workspace = true
-license.workspace = true
-
-[lints]
-workspace = true
-
-[dependencies]
-anyhow.workspace = true
-clap = { workspace = true, features = ["derive"] }
-codex-app-server-protocol.workspace = true
-serde.workspace = true
-serde_json.workspace = true
-
-[dev-dependencies]
-pretty_assertions.workspace = true