Use the new Nix Perl bindings

src/lib/Hydra/Helper/Nix.pm

@@ -4,12 +4,10 @@ use strict;
 use Exporter;
 use File::Path;
 use File::Basename;
-use Nix;
 use Hydra::Helper::CatalystUtils;
 
 our @ISA = qw(Exporter);
 our @EXPORT = qw(
-    isValidPath
     getHydraPath getHydraDBPath openHydraDB getHydraConf txn_do
     registerRoot getGCRootsDir gcRootFor
     getPrimaryBuildsForView
@@ -17,12 +15,6 @@ our @EXPORT = qw(
     getViewResult getLatestSuccessfulViewResult jobsetOverview removeAsciiEscapes);
 
 
-sub isValidPath {
-    my $path = shift;
-    return Nix::isValidPath($path);
-}
-
-
 sub getHydraPath {
     my $dir = $ENV{"HYDRA_DATA"} || "/var/lib/hydra";
     die "The HYDRA_DATA directory ($dir) does not exist!\n" unless -d $dir;