Remove the unused legacy remote compaction implementation (#44273)

## Why

Remote compaction already uses the normal Responses API, leaving the legacy `/responses/compact` runner unused.

## What changed

- Remove the legacy runner, endpoint client, request types, analytics variant, and obsolete test helpers and snapshots.
- Move tool-output trimming and its metadata tests into `compact_remote_history` for reuse by remote compaction v2.
- Consolidate retained-history filtering in the v2 implementation and remove redundant `RemoteCompactionV2` settings from tests.

## Testing

Extend the retained-history unit test to explicitly check that hook prompts survive compaction.

GitOrigin-RevId: 999bb1391aa22c3c281d6a96f98817d6c9e46ed9

codex-rs/core/src/session/tests.rs

@@ -11304,7 +11304,6 @@ async fn make_remote_compaction_session(
         move |config| {
             config.model = Some("gpt-5.2".to_string());
             config.model_provider = provider;
-            let _ = config.features.enable(Feature::RemoteCompactionV2);
             let _ = config.features.disable(Feature::TokenBudget);
         },
     )