This diff removes deprecated C++ code related to the use of `cryptopp` library.
In D5947 we are switched to using the Rust function for the signed string verification and we don't need the `cryptopp` and related C++ code base anymore.
Removing `cryptopp` from the dependencies is in the following D5949.
Linear task: [[ https://linear.app/comm/issue/ENG-2492/removing-cryptopp-from-the-tunnelbroker-and-use-rust-openssl-crate | ENG-2492 ]]