Remove schemaVersion from test recipes

[jaredlockhart]

Since the schemaVersion in test recipes will not be known when test data is written, anything we write in that field will be wrong, so maybe we should omit it from the test recipes altogether? We need to verify that clients don't depend on that field in any way first.

[lmorchard]

Looks like schemaVersion is required by the NimbueExperiment type, so when I tried removing it from the example data in my PR, the CI run failed.

Easy fix would be to make it optional in the type along with taking it out of example data, but that goes back to the verifying that clients don't depend on the field.