delete exercise 1-3 from beginner directory

...aluation_scripts/beginner/exercise_1/exercise_1_1_eval.py

...aluation_scripts/beginner/exercise_1/exercise_1_2_eval.py

...aluation_scripts/beginner/exercise_1/exercise_1_3_eval.py

...aluation_scripts/beginner/exercise_2/exercise_2_1_eval.py

...aluation_scripts/beginner/exercise_2/exercise_2_2_eval.py

...aluation_scripts/beginner/exercise_3/exercise_3_1_eval.py

...l/solution_scripts/beginner/exercise_1/exercise_1_1.ipynb

...l/solution_scripts/beginner/exercise_1/exercise_1_2.ipynb

...l/solution_scripts/beginner/exercise_1/exercise_1_3.ipynb

...l/solution_scripts/beginner/exercise_2/exercise_2_1.ipynb

...l/solution_scripts/beginner/exercise_2/exercise_2_2.ipynb

...l/solution_scripts/beginner/exercise_3/exercise_3_1.ipynb

..._ws/src/learn_environment/task_pool/task_definitions.json