mc_att_control_main: do not apply the yaw weight for the feedforward term

The meaning of the yaw weight changed with #8003:
- before, the yaw weight decreased with increasing tilt angle error, so
  it was mostly 1
- now, it is constant and depends on the tuning gains (around 0.4 by default)

It means that #8003 reduced the feedforward term, and we get the closer
behavior as before with this change.
It also reduces coupling between different parameters.