[AdmittanceController] Do we really need `admittance_tranforms_` structure

[destogl]

In some places, structure looks like intermediary storage. Maybe it is not needed, and we can use admittance_state and other structures directly. Thorough investigation required for this.

https://github.com/ros-controls/ros2_controllers/blob/f4788c594026bc3ecf0d944e1fa39f3f2d40673b/admittance_controller/include/admittance_controller/admittance_rule_impl.hpp#L191-L192