Remove AIX workaround test_subprocess (GH-8939)


An old apparent AIX behavior workaround in test_subprocess's
test_undecodable_env is no longer needed.
(cherry picked from commit 89d79b1449750b14ded0149dcdd1e39247f2c65d)

Co-authored-by: Michael Felt <aixtools@users.noreply.github.com>
2 files changed