Removes the ICrossChainMessenger interface. We don't have a strong
reason to maintain this interface and it introduces complexity to the
process of developing the SDK. With the interface, we are required to
make changes to multiple files when we simply want to change the
CrossChainMessenger class. We are also not maintaing multiple
implementations of the CrossChainMessenger that would make the interface
useful.
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>