Speed up channel processing

In particular the /pkg action is now O(lg n) instead of O(n) in the
number of packages in the channel, and listing the channel contents
no longer requires calling isValidPath() on all packages.

Derivations (and thus build time dependencies) are no longer included
in the channel, because they're not GC roots.  Thus they could
disappear unexpectedly.

src/lib/Hydra/Helper/CatalystUtils.pm

@@ -99,37 +99,6 @@ sub getBuildStats {
 }
 
 
-sub getChannelData {
-    my ($c, $builds) = @_;
-
-    my @builds2 = $builds
-	->search_literal("exists (select 1 from buildproducts where build = me.id and type = 'nix-build')")
-	->search({}, { columns => [@buildListColumns, 'drvpath', 'outpath', 'description', 'homepage'] });
-    
-    my @storePaths = ();
-    foreach my $build (@builds2) {
-        next unless isValidPath($build->outpath);
-        if (isValidPath($build->drvpath)) {
-            # Adding `drvpath' implies adding `outpath' because of the
-            # `--include-outputs' flag passed to `nix-store'.
-            push @storePaths, $build->drvpath;
-        } else {
-	    push @storePaths, $build->outpath;
-        }
-        my $pkgName = $build->nixname . "-" . $build->system . "-" . $build->id;
-        $c->stash->{nixPkgs}->{"${pkgName}.nixpkg"} = {build => $build, name => $pkgName};
-        # Put the system type in the manifest (for top-level paths) as
-	# a hint to the binary patch generator.  (It shouldn't try to
-	# generate patches between builds for different systems.)  It
-	# would be nice if Nix stored this info for every path but it
-	# doesn't.
-	$c->stash->{systemForPath}->{$build->outpath} = $build->system;
-    };
-
-    $c->stash->{storePaths} = [@storePaths];
-}
-
-
 sub error {
     my ($c, $msg) = @_;
     $c->error($msg);