This is not part of High Sierra, but can you go open up Keychain Access and go to Preferences within there and in the General tab you should have a "Show Keychain status on Menu Bar" option. If so, uncheck that and the lock will disappear.
I don't use it, but I see you have Dashlane on the top bar. Could it be from that? (Clutching at straws here.)
It works the same as dragging an App off the Dock. It's no longer there.
When it says Lock Screen and Lock Keychain, Open Security Preference and Open Keychain Access, I assumed its in System Preference....dont see any ..
EDIT:
Oppps, I guess I should have updated the page before posting and I would have seen the problem had been fixed it seems.
Yes I dragged it off the menu bar, it works. Thanks