Remove slave from validation when detaching it
Remove slave from validation when detaching it

When detaching a slave, remove it from the validation values. Without this,
if it were invalid before detaching, it would make the view invalid and
without the possibility to correct it, since the invalid widgets would not be
there anymore.

Change-Id: Ib2e96a5eff14e18f0bbbdeff7cbc0568aa780933

stoq/kiwi