Drop explicit JSON dependency

Dependencies

• [2] AWZEBCMS Use the JSON module
• [3] TH674WKJ add log diff to compare logs to previous builds
• [4] AMFMXR52 Provide a command ‘hydra-init’ to initialise/upgrade the database
• [*] SAFVRDTK * Put Hydra's dependencies so that they can easily be installed in a

Change contents

• edit in deps.nix at line 25
  [3.385]→[2.0:50](∅→∅)
  − perlPackages.JSON # FIXME: JSON::XS should work