Switch back to built-in Julia threads

src/auxiliary/auxiliary.jl

@@ -224,15 +224,15 @@ macro threaded(expr)
     # standard library with an additional check whether only a single thread is used
     # to reduce some overhead (and allocations) for serial execution.
     #
-    # return esc(quote
-    #   let
-    #     if Threads.nthreads() == 1
-    #       $(expr)
-    #     else
-    #       Threads.@threads $(expr)
-    #     end
-    #   end
-    # end)
+    return esc(quote
+      let
+        if Threads.nthreads() == 1
+          $(expr)
+        else
+          Threads.@threads $(expr)
+        end
+      end
+    end)
     #
     # However, the code below using `@batch` from Polyester.jl is more efficient,
     # since this packages provides threads with less overhead. Since it is written
@@ -241,10 +241,11 @@ macro threaded(expr)
     # them) available in Julia.
     # !!! danger "Heisenbug"
     #     Look at the comments for `wrap_array` when considering to change this macro.
-
+    #=
     return esc(quote
                    Trixi.@batch $(expr)
                end)
+    =#               
 end
 
 #     @trixi_timeit timer() "some label" expression