Remove non-public data from examples

Some of the examples use non-public data. In the short term it's not an issue as the Shared Drive is not Public. Long term when finalizing the examples, we will need to only provide public data for examples, or instructions for how to obtain the needed data.

TODO:
- [ ] Zindi data can be obtained from Zindi.org by anyone who signs up for an account
- [x] Crop Yield data can't be shared, we should probably delist that notebook from the public index, and remove the data from the shared drive.