test: remove using md5 from pgproto tests

sbroad

test/int/test_plugin.py

test/int/test_sql.py

test/pgproto/auth_test.py

test/pgproto/datetime_test.py

test/pgproto/extended_query_test.py

test/pgproto/pipelining_test.py

test/pgproto/plugin_test.py

test/pgproto/psql_session_from_the_guide_test.py

test/pgproto/simple_query_test.py

test/pgproto/ssl_test.py

test/pgproto/storage_limits_test.py

test/pgproto/tab_completion_test.py

test/pgproto/types_test.py

test/pgproto/user_can_read_from_query_cache_test.py