Removes forward declaration from ddDrakeModel.h (since now RBTd is a typedef from RBT.h)
Removes forward declaration from ddDrakeModel.h (since now RBTd is a typedef from RBT.h)

patmarion/director,patmarion/director,patmarion/director,openhumanoids/director,patmarion/director,openhumanoids/director,manuelli/director,manuelli/director,mitdrc/director,openhumanoids/director,openhumanoids/director,openhumanoids/director,manuelli/director,manuelli/director,patmarion/director,mitdrc/director,mitdrc/director,mitdrc/director,manuelli/director,mitdrc/director