Remove shift and rotmat attributes from Curve class

[ddudt]

These attributes are redundant with the other optimizable parameters for each curve type, and it is getting cumbersome to maintain the special logic for them. They were intended to make it easier to initialize coil geometries, but this might be obsolete now with other utility functions we have added. These attributes are mostly hidden from the user, so removing them would not change the UI.

[dpanici]

Why again can we not just have these as attribute and passed in as transforms?

[f0uriest]

Because for a coilset, we only have one set of transforms, but the shift and rotmat can be different for each coil, so they have to be in params

[dpanici]

Keep as params for just FourierRZCoil (and FourierRZCurve)

[dpanici]

But we should just get rid of it for all curves