CatalystUtils.pm: don't use Hydra::Helper::Nix

Using it causes database information to get fixated early, before tests can set a
new database. We only used it in one case, and that is an absolute reference anyway. The
tests for channel generation are passing, and that uses
[requireLocalStore, so this should be fine.

src/lib/Hydra/Helper/CatalystUtils.pm

@@ -6,7 +6,6 @@ use warnings;
 use Exporter;
 use ReadonlyX;
 use Nix::Store;
-use Hydra::Helper::Nix;
 
 our @ISA = qw(Exporter);
 our @EXPORT = qw(
@@ -414,6 +413,7 @@ sub approxTableSize {
 
 sub requireLocalStore {
     my ($c) = @_;
+    require Hydra::Helper::Nix;
     notFound($c, "Nix channels are not supported by this Hydra server.") if !Hydra::Helper::Nix::isLocalStore();
 }