Revert "test: add test for prefix unit loading"

Revert "test: add test for prefix unit loading"

This reverts commit 7ce49e656b1377713ade999dfe381807a78313cd.

The previous revert (6927aa2bc09726ff1f071770a8ce0c2ea6430b6b)
reverts more than it is described within its description. As it is
a base for some of subsequent commits in the upstream, they are
silently removed, probably because of conflict resolving.

Prefix unit loading is a feature that is a victim of such silent removal.
Therefore, the feature test is also (temporarily, I hope) removed with
this commit.

Change-Id: Ie82e5a54852ea08c8b3f0561f304fab6f3434aaf