Power recycling optimization is inaccessible

The ifo_power function has a keyword argument PRfixed that determines whether it optimizes the PRM transmission.

It was once controlled by a PRfixed argument in the gwinc function. That kwarg still exists, but no longer does anything. In fact, there's no longer any high-level interface to turn on this calculation, though you can still invoke it by calling ifo_power and then updating the parameter by hand.

Should we have a nicer interface to this feature? If so, what should it be? And what to do about the vestigial gwinc function?