[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/tests/common/test_codex.rs

@@ -189,17 +189,13 @@ fn docker_command_capture_stdout<const N: usize>(args: [&str; N]) -> Result<Stri
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
 pub enum ApplyPatchModelOutput {
     Freeform,
-    Shell,
-    ShellViaHeredoc,
     ShellCommandViaHeredoc,
 }
 
 /// A collection of different ways the model can output an apply_patch call
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
 pub enum ShellModelOutput {
-    Shell,
     ShellCommand,
-    LocalShell,
     // UnifiedExec has its own set of tests
 }
 
@@ -959,9 +955,7 @@ impl TestCodexHarness {
             ApplyPatchModelOutput::Freeform => {
                 Box::pin(self.custom_tool_call_output(call_id)).await
             }
-            ApplyPatchModelOutput::Shell
-            | ApplyPatchModelOutput::ShellViaHeredoc
-            | ApplyPatchModelOutput::ShellCommandViaHeredoc => {
+            ApplyPatchModelOutput::ShellCommandViaHeredoc => {
                 Box::pin(self.function_call_stdout(call_id)).await
             }
         }