calc_bias contains a missing import and is unused

[braingram]

stcal/src/stcal/ramp_fitting/likely_algo_classes.py

Line 251 in 787aa81

def calc_bias(self, countrates, sig, cvec, da=1e-7):

contains attempted uses of fit_ramps:

stcal/src/stcal/ramp_fitting/likely_algo_classes.py

Line 289 in 787aa81

result_low_a = fit_ramps(z, self, sig, countrateguess=countrates)

which is undefined.

As we haven't seen any errors it's likely calc_bias is unused.

It's unclear to me if this is a bug (and it should be used) or if the test coverage is incomplete and we may see failures during non-test runs.