move unrelated unit tests away from MG

[plebhash]

during #949 we re-activated some unit tests inside utils/message-generator/src/main.rs

while reviewing this PR I noticed multiple unit tests have no correlation with MG code:

• test_serialise_and_deserialize
• test_serialize_and_deserialize_2_oemc
• test_serialize_and_deserialize_3_oemcs
• test_serialize_and_deserialize_4_nemj
• test_serialize_and_deserialize_5_scmj
• test_serialize_and_deserialize_6_dmj
• test_serialize_and_deserialize_7_nmj
• it_send_and_receive
• it_create_tests_with_different_messages

I assume they were started inside utils/message-generator/src/main.rs during the development of MG, but it feels wrong to keep them there, since they never touch any actual MG code

so they should probably be moved to appropriate crates

[Fi3]

all the serialize and deserialize tests, test the json deserialization, and the serializtion with serde_sv2 lib. We can likley move them them somewhere else, but we should keep them.

it_send_and_receive, test the setup_as_upstream and setup_as_downstream functions at a first look seems ok to have them where they are.

it_create_tests_with_different_messages this seems something that I put there while developing and then forgotten there? maybe could go in roles_logic_sv2 but not sure it could make sens also to just remove it. @lorbax ?