UT does not require PiecewiseTrajectory

This part of a campaign to remove the use of PiecewiseTrajectory. The other half is to replace the use of PiecewiseTrajectory in TT, which needs a trajectory which consists of between 1 and 4 LineTraj equivalent. Reason to deprecate PiecewiseTrajectory is the fact that it is a recursive data structure (it is a Trajectory that consists of a number of other Trajectories) and as such it is not suited for use inside an std::variant, blocking the use of std::variant for measurements.