thorium: switch to the default queue aross the board

Link: https://github.com/GeneAssembly/biosal/issues/819
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
thorium: don't use queue iterator

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
thorium_worker_pool: use default queue

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>