This reverts https://review.gerrithub.io/#/c/393980/ which was
a temporary workaround to unblock the Deckhand gate. pifpaf should
be used to run unit tests as having to install Docker just to kick
off unit tests is excessive.
However, the unit-tests.sh script is maintained in tools/ directory
as a fallback.
Change-Id: I24a10d4b3ea00006004f27d0086719fb0bf86dd9