[codex] Remove unused legacy shell tools (#22246)

## Why

Recent session history showed no active use of the raw `shell`,
`local_shell`, or `container.exec` execution surfaces. Keeping those
handlers/specs wired into core leaves duplicate shell execution paths
alongside the supported `shell_command` and unified exec tools.

## What changed

- Removed the raw `shell` handler/spec and its `ShellToolCallParams`
protocol helper.
- Removed the legacy `local_shell` and `container.exec` handler/spec
plumbing while preserving persisted-history compatibility for old
response items.
- Normalized model/config `default` and `local` shell selections to
`shell_command`.
- Pruned tests that exercised removed raw-shell/local-shell/apply-patch
variants and kept coverage on `shell_command`, unified exec, and
freeform `apply_patch`.

## Verification

- `git diff --check`
- `cargo test -p codex-protocol`
- `cargo test -p codex-tools`
- `cargo test -p codex-core tools::handlers::shell`
- `cargo test -p codex-core tools::spec`
- `cargo test -p codex-core tools::router`
- `cargo test -p codex-core
active_call_preserves_triggering_command_context`
- `cargo test -p codex-core guardian_tests`
- `cargo test -p codex-core --test all shell_serialization`
- `cargo test -p codex-core --test all apply_patch_cli`
- `cargo test -p codex-core --test all shell_command_`
- `cargo test -p codex-core --test all local_shell`
- `cargo test -p codex-core --test all otel::`
- `cargo test -p codex-core --test all hooks::`
- `just fix -p codex-core`
- `just fix -p codex-tools`

sdk/typescript/tests/abort.test.ts

@@ -127,7 +127,7 @@ describe("AbortSignal support", () => {
             void event; // Consume the event
             eventCount++;
             // Abort after first event
-            if (eventCount === 5) {
+            if (eventCount === 1) {
               controller.abort("Aborted during iteration");
             }
             // Continue iterating - should eventually throw

sdk/typescript/tests/responsesProxy.ts

@@ -181,15 +181,14 @@ export function assistantMessage(text: string, itemId: string = DEFAULT_MESSAGE_
 }
 
 export function shell_call(): SseEvent {
-  const command = ["bash", "-lc", "echo 'Hello, world!'"];
   return {
     type: "response.output_item.done",
     item: {
       type: "function_call",
       call_id: `call_id${Math.random().toString(36).slice(2)}`,
-      name: "shell",
+      name: "shell_command",
       arguments: JSON.stringify({
-        command,
+        command: "echo 'Hello, world!'",
         timeout_ms: 100,
       }),
     },