Why do you think that you are no longer Diabetic ?
The most likely way to discover this amazing fact would be to have an HbA1c test, and have a result showing a non diabetic reading, but you would probably want more than one result over an extended period.
In regard to the Metformin, I would think you can stop taking that whenever you wish, as nobody can be forced to take any medication against their will, but it would be better to at least discuss this with your GP first. Metformin itself is only a very small help, and diet and exercise will be the main drivers towards reducing your Blood Glucose.