smq2Q_XY modelpack gates includes the CPhase gate

[eendebakpt]

Describe the bug

The model pack smq2Q_XY includes the CPhase in the description and the gates, but it is not used in the germs or fiducials.

https://github.com/sandialabs/pyGSTi/blob/d27e4e688a64914a0b7aaec1de91aa56f7ce70c2/pygsti/modelpacks/smq2Q_XY.py#L20-L23

Also the smq2Q_XYI description contains a reference to the CPhase (and many some more modelpacks).

Expected behavior

I believe the smq2Q_XY should not contain any references to CPhase. And maybe the docstrings could be expanded to describe the model and its uses in more detail.

Environment (please complete the following information):

• pyGSTi version [e.g. v0.9.7.4]: Current master branch
• python version [e.g. 3.7, 2.7]: Any
• OS [e.g. OSX 10.14, Ubuntu 16.04 LTS]: Any