Stop advertising shell snapshots from local exec servers (#39958)

Set the local exec-server's `shellSnapshotV2` capability to `false` on all
platforms.

GitOrigin-RevId: 4faca33e62b736e7cd2b9587e7992b0723f915fb

codex-rs/exec-server-protocol/src/protocol.rs

@@ -186,7 +186,7 @@ impl EnvironmentInfo {
                 capability_discovery_sandbox: true,
                 environment_config_read: true,
                 sandboxed_file_streaming: true,
-                shell_snapshot_v2: cfg!(unix),
+                shell_snapshot_v2: false,
             },
         }
     }