Always add PhoneWindow when creating DecorView.

Because DecorView is now a static inner class, we need to remember to
always add the PhoneWindow on which it depends.
PhoneWindow.generateDecor will do that now to prevent further
mistakes.

Also remove PhoneWindow.setFeatureFromAttrs which is not used
anywhere and seems to be an artifact from the past.

Bug: 25086413
Change-Id: I0d8e5df717d7046e85ffc58f7ec4e94ce15a7d80