[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/tools/src/tool_spec.rs

@@ -25,8 +25,6 @@ pub enum ToolSpec {
         description: String,
         parameters: JsonSchema,
     },
-    #[serde(rename = "local_shell")]
-    LocalShell {},
     #[serde(rename = "image_generation")]
     ImageGeneration { output_format: String },
     // TODO: Understand why we get an error on web_search although the API docs
@@ -58,7 +56,6 @@ impl ToolSpec {
             ToolSpec::Function(tool) => tool.name.as_str(),
             ToolSpec::Namespace(namespace) => namespace.name.as_str(),
             ToolSpec::ToolSearch { .. } => "tool_search",
-            ToolSpec::LocalShell {} => "local_shell",
             ToolSpec::ImageGeneration { .. } => "image_generation",
             ToolSpec::WebSearch { .. } => "web_search",
             ToolSpec::Freeform(tool) => tool.name.as_str(),