Remove obsolete Builds columns and provide accurate "Running builds"

This removes the "busy", "locker" and "logfile" columns, which are no
longer used by the queue runner. The "Running builds" page now only
shows builds that have an active build step.

src/lib/Hydra/Helper/AddBuilds.pm

@@ -450,8 +450,6 @@ sub checkBuild {
             , nixexprpath => $jobset->nixexprpath
             , priority => $buildInfo->{schedulingPriority}
             , finished => 0
-            , busy => 0
-            , locker => ""
             , iscurrent => 1
             , ischannel => $buildInfo->{isChannel}
             });