Remove redundant check

Dependencies

• [2] VU2OLHD2 Move most of AddBuilds to hydra-eval-jobset
• [3] N22GPKYT * Put info about logs / build products in the DB.
• [4] HP5WJLQU hydra-eval-{jobs,jobset}: Pass file name as <...>

Change contents

• edit in src/script/hydra-eval-jobset at line 359
  [2.11277]→[2.11277:11433](∅→∅)
  − die "multiple alternatives for the input containing the Nix expression are not supported.\n"

  − if scalar @{$inputInfo->{$nixExprInputName}} != 1;