Is your feature request related to a problem? Please describe.
The visibility of the legend should be based on the consumer not dictated by the library.

Describe the solution you'd like
Remove this toggle:

In favor of just providing a simple prop for legend visibility where then the consumer can hook up their own button or service to provide that visibility.

Checklist

• this request is checked against already exist requests
• [ ] every related Kibana issue is listed under Kibana Cross Issues list
• [ ] kibana cross issue tag is associated to the issue if any kibana cross issue is present