Remove redundant hard coded replication parameters

The following new `mysql` class replication parameters were added in 0.8.1, however the existing hard coded parameters were not removed from the my.conf.erb template:

- `expire_logs_days`
- `max_binlog_size`

Sorry about the noise with the previous pull request, I saw it failed the tests because I moved the parameters. I didn't see any test for these lines which would be removed so this should be OK. This is my first ever pull request so I was always bound to make a mistake!