fix: remove memory leak from reverse_binary_tree.cpp

[vil02]

Description of Change

This PR adds a destructor to BinaryTree. Furthermore the copy constructor and the assignment operator was explicitly deleted in order to... simplify things.

Checklist

• Added description of change
• Added file name matches File name guidelines
• Added tests and example, test must pass
• Added documentation so that the program is self-explanatory and educational - Doxygen guidelines
• Relevant documentation/comments is changed or added
• PR title follows semantic commit guidelines
• Search previous suggestions before making a new one, as yours may be a duplicate.
• I acknowledge that all my contributions will be made under the project's license.

Notes:
Removes the memory leak from reverse_binary_tree.cpp.