Remove methods on DCMotor and ContinuousServo

[dhalbert]

DCMotor and ContinuousServo, but not regular Servo, provide a deinit() operation that sets .throttle to 0. However, they don't actually deinit anything: you could change the speed again in the future.

I'm not sure why they were added (they were in from the start). I think we could just delete them.

Came up while @caternuson was recoding an Arduino example (see #17), but this is a separate issue.

Tagging @tannewt for any comment.

[tannewt]

I'm ok if you want to remove it. They are there to match how you use other CircuitPython classes. Either way is fine.

[geekguy-wy]

I will remove them. PR #37 fixes this

[FoamyGuy]

This PR was merged, closing the issue.