Don't fail early when -j0 is passed

If the build closure contains some CA derivations, then we can't know
ahead-of-time that we won't build anything as early-cutoff might come-in
at a laster stage

src/libstore/build/worker.cc

@@ -223,11 +223,6 @@ void Worker::run(const Goals & _topGoals)
     uint64_t downloadSize, narSize;
     store.queryMissing(topPaths, willBuild, willSubstitute, unknown, downloadSize, narSize);
 
-    if (!willBuild.empty() && 0 == settings.maxBuildJobs && getMachines().empty())
-        throw Error(
-            "%d derivations need to be built, but neither local builds ('--max-jobs') "
-            "nor remote builds ('--builders') are enabled", willBuild.size());
-
     debug("entered goal loop");
 
     while (1) {