Remove python2 and mysql5.7 code

[mirageoasis]

while looking around repository I came across python2, mysql 5.7 tests, codes
and Github Actions which was deprecated in python-mysql-replication version 1.0

However, I think there should be some improvement over config.json and docker-compse.yml

Since config.json port setting depends on docker-compose file.

[sean-k1]

If you delete all mysql 5.7 version Test
it would be better set global variable binlog_row_metadata = "FULL" in setUp method.

[mirageoasis]

If you delete all mysql 5.7 version Test it would be better set global variable binlog_row_metadata = "FULL" in setUp method.

understood I will apply this in following commit

[dongwook-chan]

We cannot overlook the MySQL 5.7 user base. I know MySQL declared EOL for 5.7 but there are plenty of users that can benefit from the code.