nix1: don't deliver perl-bindings of nixStable (a.k.a nix2)

This causes collisions between the build outputs of `nix` when building
in an environment with `nix1.perl-bindings` and `nix`:

```
collision between `/nix/store/aa4rrcj7dg2xj4rfkiclcmp745ibqng0-nix-2.0.4/lib/libnixstore.so' and `/nix/store/sp0sdi4bll80h58big1iy8kkh3qqxpw2-nix-1.11.16/lib/libnixstore.so'
builder for '/nix/store/wgbccin107lhm8cv9imnnvkx1j2pgibc-hydra-perl-deps.drv' failed with exit code 25
```