[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`

codex-rs/core/src/tools/router_tests.rs

@@ -110,7 +110,7 @@ async fn parallel_support_does_not_match_namespaced_local_tool_names() -> anyhow
         },
     );
 
-    let parallel_tool_name = ["shell", "local_shell", "exec_command", "shell_command"]
+    let parallel_tool_name = ["exec_command", "shell_command"]
         .into_iter()
         .find(|name| {
             router.tool_supports_parallel(&ToolCall {
@@ -399,7 +399,6 @@ fn namespace_function_names(specs: &[ToolSpec], namespace_name: &str) -> Vec<Str
             ToolSpec::Function(_)
             | ToolSpec::Freeform(_)
             | ToolSpec::ToolSearch { .. }
-            | ToolSpec::LocalShell {}
             | ToolSpec::ImageGeneration { .. }
             | ToolSpec::WebSearch { .. }
             | ToolSpec::Namespace(_) => None,