Revert "Use a ThreadPoolExecutor to concurrently store files dut string import (#1427)" (#1428)
Revert "Use a ThreadPoolExecutor to concurrently store files dut string import (#1427)" (#1428)

This reverts commit 2245df85f4315503462800c30efd9ee683331fe5.
ajvpot/CTFd,LosFuzzys/CTFd,ajvpot/CTFd,isislab/CTFd,CTFd/CTFd,isislab/CTFd,LosFuzzys/CTFd,ajvpot/CTFd,ajvpot/CTFd,LosFuzzys/CTFd,CTFd/CTFd,isislab/CTFd,LosFuzzys/CTFd,CTFd/CTFd,CTFd/CTFd,isislab/CTFd