Non lenses

We need to remove these non-lenses.  I'm not completely happy with the solution here.  Suggestions?  Some other options include:

* make `_theta` a plain function instead of a Getter (see commit msg for counterpoint)
* drop the `HasTheta` class, but keep a monomorphic `_theta` for the 15-20 uses in this library (due to changed `direction`)
* rename `_theta`