Remove exported mocks

> Exported, generated mocks should be deleted. I don't see the need to have these exported if their purpose is testing for this SDK. Example: https://github.com/open-feature/go-sdk/blob/main/openfeature/hooks_mock.go

Remove exported generated mocks. These are for internal testing.

If there is real testing utils we want to export, we should put them in a `/testing` package.