[3.13] gh-98552: Revert (unneeded, already done elsewhere) "flush std streams in the multiprocessing forkserver before fork (GH-141849)" (GH-141871)

[3.13] gh-98552: Revert (unneeded, already done elsewhere) "flush std streams in the multiprocessing forkserver before fork (GH-141849)" (GH-141871) #220440