I reverted your mysql service file change. The script is definitely needed because it's the only way for systemd to know when mysql is actually ready. Without this, services relying on mysql being available are started too early and may fail because mysql isn't ready yet.
- After=syslog.target is obsolete
- I'm pretty sure your ExecStop= is also unnecessary because afaik this is what systemd does by default
- Group= would default to mysql with User=mysql being set, so it's not needed as well
please don't just remove/edit stuff if you don't know why it is there in the first place.