Unpin camera_android and remove its only usage (flutter#150017)

Fixes flutter#146004

The `camera_android`plugin had its version pinned when it was still used in the `gradle_deprecated_settings`. It has since been [replaced](flutter#148426) by `camera_android_camerax`, and therefore isn't used in `flutter/flutter`. So it's pin should be fine to remove.

Author: gmackall