This removes the last creation of foreground tasks in the compilation
state. I think this logic can be removed completely, because
a) the number of background tasks is already capped at {max(1,
   FLAG_wasm_num_compilation_tasks)}, and
b) in order to get predictable timing you can use the --predictable
   flag which makes all background tasks execute synchronously with
   foreground tasks (from the same queue).

R=ahaas@chromium.org
CC=mstarzinger@chromium.org

Bug: v8:8050, v8:8689
Change-Id: I142af6b42f9bb9befc7c7b7d6002192d72bd7677
Reviewed-on: https://chromium-review.googlesource.com/c/1451841
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59341}