Stop shipping codex-exec-server in release artifacts (#57628)

## What changed

- Remove the standalone executor from CLI and app-server packages, release binary lists, and Bazel runtime archives.
- Remove the package builder's `--exec-server-bin` option and `execServer` metadata, along with executor-specific installer checks, signing configuration, and package smoke tests.
- Keep the standalone executor available to build from source.

GitOrigin-RevId: ada4c92c092e3c7a3067129913e99f4606f7adc8

scripts/codex_package/targets.py

@@ -45,7 +45,6 @@ class PackageVariant:
 class PackageInputs:
     entrypoint_bin: Path
     code_mode_host_bin: Path
-    exec_server_bin: Path
     rg_bin: Path
     bwrap_bin: Path | None
     codex_command_runner_bin: Path | None