[705-wipe_data-sh-and-other-upgrade_-scripts-do-not-set-prefix] Revert "[705-wipe_data-sh-and-other-upgrade_-scripts-do-not-set-prefix] Protected dhcp_test_lib.sh against unset ${prefix} and fixed includers"

This reverts commit 7fe457cb301772093ff7002c9a3be12b25f7d73b.

Reviewer asked this to be reverted as overkilling.