Remove control_cost() method from Walker2d and Hopper when gymnasium v5 environments are released

[rickstaa]

Is your feature request related to a problem? Please describe.

Currently, in the Walker2d and Hopper we have to recalculate the ctrl_cost since it is not passed to the info dictionary. This has already been solved in Farama-Foundation/Gymnasium#572 but has yet to be released. When the v5 environment is released the following code can be removed:

stable-gym/stable_gym/envs/mujoco/hopper_cost/hopper_cost.py

Line 276 in fb3cee7

ctrl_cost = super().control_cost(action)

stable-gym/stable_gym/envs/mujoco/walker2d_cost/walker2d_cost.py

Line 271 in fb3cee7

ctrl_cost = super().control_cost(action)

Describe the solution you'd like

No response

Describe alternatives you've considered

No response

Additional context

We should double-check the keys found in the info dictionary when the v5 environments are released.