Revert "ztest fails assertion in zio_write_gang_member_ready()"

This reverts commit 0156253d29a303bdcca3e535958e754d8f086e33.

That commit was identified as causing IO errors on a user's
encrypted dataset:
https://github.com/openzfs/zfs/issues/14413

Signed-off-by: Tony Hutter <hutter2@llnl.gov>