unused lines of code in `glm.py` and `varfuncs.py`

[jGaboardi]

Unused lines of code:

• spglm/glm.py#L342
  • model = self.model
• spglm/varfuncs.py#L117
  • from statsmodels.tools.numdiff import approx_fprime_cs

[jGaboardi]

See more conversation for `spglm/varfuncs.py#L117 in https://github.com/pysal/spglm/pull/40#discussion_r1355249720