By:
* Add .gitkeep to retain test fixture directories under
./python/testdata
* Move GitHub related functionality to ./experimental (it is not in use)
* Comment out test in ./cmd/sync
* Fix test in ./git
Unexported fields are skipped during marshalling, so this would be a
nop.
The code in `./cmd/sync/github*.go` is currently unused.
Confirmed that staticcheck passes when run with:
```
staticcheck -checks SA9005 ./...
```
Functionality from `io/ioutil` has moved to the `io` and `os` packages
in go1.16 ([reference](https://pkg.go.dev/io/ioutil)).
Confirmed that staticcheck passes when run with:
```
staticcheck -checks SA1019 ./...
```