Remove all instances of the word "iff"

Remove all instances of the word "iff"

It's elitist mathematical jargon. In all cases dealt with here, it adds
no additional meaning compared to "if", beyond what was already obvious
from context. Thus, its only purpose is to smugly demonstrate that the
author attended their second-year mathematics classes, at the expense of
causing confusion for everyone who doesn't have such a background.

If you really think you need to convey extra information beyond what
"if" gives you, the English language contains plenty of devices for doing
so, without resorting to neologisms.

Change-Id: Iae21095d02ec2935c10e94f532235c2671c115b1