Protocol env: remove legacy logging interface.

Context

The logging interface available to the Protocol is now deprecated and its use is discouraged. There has been some effort made recently to remove it entirely throughout the codebase. On top of that the protocol does not really use it, so it's reasonable to remove it. We should probably consider replacing it with another, more modern interface, based on Internal_event module, but perhaps even this is not really needed. Therefore for now I just removed the existing interface. I might create a new one if that's needed.

Manually testing the MR

Verify that the code still compiles after removing logging.

Checklist

• Consider replacing legacy logging with a new interface.