testing: remove refs to test_nix in run-all.sh
testing: remove refs to test_nix in run-all.sh

Somewhere in the last set of changes, a few references to
`test_nix` were not removed.  Since that function doesn't exist,
the tests would never be run on those targets.

This script is only used when testing locally right now.

Signed-off-by: Paul Osborne <b6afffd6c1a00645fdd04b09edf63d034a949a39@gmail.com>

Susurrus/nix,nix-rust/nix,xd009642/nix,xd009642/nix,MarkusJais/nix-rust,geofft/nix-rust,MarkusJais/nix-rust,posborne/rust-nix,nikklassen/nix-rust,MarkusJais/nix-rust,berkowski/nix,posborne/rust-nix,nix-rust/nix,geofft/nix-rust,berkowski/nix,berkowski/nix,Susurrus/nix,kamalmarhubi/nix-rust,geofft/nix-rust,kamalmarhubi/nix-rust,nikklassen/nix-rust,asomers/nix,nikklassen/nix-rust,posborne/rust-nix,carllerche/nix-rust,carllerche/nix-rust,Susurrus/nix,carllerche/nix-rust,asomers/nix,xd009642/nix,kamalmarhubi/nix-rust