Removed some never-implemented method declarations regarding Motions.
Removed some never-implemented method declarations regarding Motions.

elen4/simbody,scamille/simbody,scamille/simbody,robojukie/simbody,elkingtonmcb/simbody,elkingtonmcb/simbody,Gjacquenot/simbody,chrisdembia/simbody,simbody/simbody,elen4/simbody,Gjacquenot/simbody,robojukie/simbody,chrisdembia/simbody,chrisdembia/simbody,robojukie/simbody,elkingtonmcb/simbody,Gjacquenot/simbody,simbody/simbody,scamille/simbody