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/lib.rs

@@ -29,11 +29,6 @@ pub use responses_metadata::CodexResponsesMetadata;
 pub use turn_metadata::detached_memory_responses_metadata;
 mod codex_thread;
 mod compact_model_fallback;
-#[expect(
-    dead_code,
-    reason = "the unrouted v1 runner is removed in the follow-up"
-)]
-mod compact_remote;
 mod compact_remote_history;
 mod compact_remote_v2;
 mod compact_token_budget;