Remove nix from hydra-perl-deps

Also add nix to passthru. This makes it easier to override nix in 'nix develop', e.g.

$ nix develop
–redirect .#hydraJobs.build.x86_64-linux.nix ~/Dev/nix/outputs/out
–redirect .#hydraJobs.build.x86_64-linux.nix.dev ~/Dev/nix/outputs/dev

Created by  Eelco Dolstra  on October 20, 2020
7HFOCQ2HMWFMHEQEH673QALNMDWCTAGA4X3DMUTL23ZIDX2BV5KQC
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