Move most of AddBuilds to hydra-eval-jobset

Having this stuff in a separate module is a remnant of the time when
hydra-server could add builds to the queue directly. This is no longer
the case.

tests/Setup.pm

@@ -4,7 +4,6 @@ use strict;
 use Exporter;
 use Hydra::Helper::Nix;
 use Hydra::Model::DB;
-use Hydra::Helper::AddBuilds;
 use Cwd;
 
 our @ISA = qw(Exporter);

tests/evaluation-tests.pl

@@ -1,7 +1,6 @@
 use strict;
 use Hydra::Schema;
 use Hydra::Model::DB;
-use Hydra::Helper::AddBuilds;
 use Cwd;
 use Setup;