Charge sign is redundant in LoopHelix and CentralHelix parameterizations

[brownd1978]

The sign of the charge is redundantly configured in the helix parameterizations. This can cause inconsistencies for nearly-straight tracks for which the geometric curvature could change sign (due to statistical fluctuation). The interface and payload should be updated to derive charge sign only from the geometric parameter. Note the magnitude of the charge must still be supplied externally, as that cannot be determined from the fit. It should be stored as unsigned.