Not possible to use yaw from GPS Velocity estimator for ground rovers

[lukegluke]

As documentation says: This also makes it possible to operate without any magnetometer data or dual antenna GPS receiver for yaw provided some horizontal movement after takeoff can be performed to enable the yaw to become observable.

Yaw EKFGSF estimator is updated only when _control_status.flags.in_air is set https://github.com/PX4/ecl/blob/f62662ee4688dfc3f1712b50900ef03c9ff55ceb/EKF/ekf_helper.cpp#L1775 This criteria is not relevant for ground rovers, while yaw estimation from GPS without magnetometer is really useful.

[priseborough]

I'm not sure if rovers will have enough horizontal acceleration to enable the GSF to estimate yaw. This will likely require a different mode of yaw alignment and estimation where the assumption of zero sideslip is used.