check_cals script handling of biases

[MNBrod]

When check_cals is used on a night of data, if there is a configuration for which only biases were collected (generally only happens accidentally/in error), the script reports that all science files in the matching binning have incomplete calibrations (since a given set of biases are applicable to a wide range of science files).

The script should ignore configurations in which there are only bias frames.