Remove old SKY and OTF mode code from agActor

The OTF (guide objects from gaia database) and SKY (guide objects from an image) modes are not currently being used and the code has become stale w.r.t. everything else. This stale code is confusing for development of new features and makes existing features difficult to maintain without the code becoming even more stale.

INSTRM-2684 is a ticket for making the OTF mode work again although Robert has expressed a desire to see the entire implementation of that mode re-done.

There has not been an interest in getting the SKY mode working again but if so it would almost be easier to start from a tabula rasa regardless.

For this ticket the branching logic for these two modes should be removed from the control loop.