Remove Switch dependency, we're not using it

Dependencies

• [2] 6K5PBUUN Use buildEnv to combine Hydra's Perl dependencies
• [3] HPIJ35SG
• [*] T4LLYESZ * Nix expression for building Hydra.

Change contents

• edit in release.nix at line 87
  [2.960]→[2.960:1031](∅→∅)
  − Switch # XXX: seems to be an indirect dep of `hydra-build'