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/cli.py

@@ -140,11 +140,6 @@ def create_parser() -> argparse.ArgumentParser:
             "the host is built with Cargo."
         ),
     )
-    parser.add_argument(
-        "--exec-server-bin",
-        type=Path,
-        help="Optional prebuilt codex-exec-server executable. If omitted, build it with Cargo.",
-    )
     parser.add_argument(
         "--bwrap-bin",
         type=Path,
@@ -215,11 +210,6 @@ def assemble_package(args: argparse.Namespace) -> Path:
             "prebuilt code-mode host executable",
             "--code-mode-host-bin",
         ),
-        exec_server_bin=resolve_optional_input_path(
-            args.exec_server_bin,
-            "prebuilt executor executable",
-            "--exec-server-bin",
-        ),
         bwrap_bin=resolve_optional_input_path(
             args.bwrap_bin,
             "prebuilt Linux bwrap executable",
@@ -239,7 +229,6 @@ def assemble_package(args: argparse.Namespace) -> Path:
     inputs = PackageInputs(
         entrypoint_bin=source_outputs.entrypoint_bin,
         code_mode_host_bin=source_outputs.code_mode_host_bin,
-        exec_server_bin=source_outputs.exec_server_bin,
         rg_bin=resolve_rg_bin(spec, args.rg_bin),
         bwrap_bin=source_outputs.bwrap_bin,
         codex_command_runner_bin=source_outputs.codex_command_runner_bin,
@@ -250,7 +239,6 @@ def assemble_package(args: argparse.Namespace) -> Path:
     for filename, prebuilt in (
         (variant.entrypoint_name(spec), args.entrypoint_bin),
         (f"codex-code-mode-host{spec.exe_suffix}", args.code_mode_host_bin),
-        (f"codex-exec-server{spec.exe_suffix}", args.exec_server_bin),
     ):
         if args.strip == "all" or (
             args.strip == "auto"