
It is no longer directly used by any test code in this repository since
we switched to stestr[1].
It is now installed as a dependency of stestr.
Also remove the note about behavior of old pip, because recent pip can
resolve dependencies without requiring a specific order.
[1] 22e10bc884
Change-Id: I14c166abd63ded5c63275e6e536286d62fda4f12