Clear the store's learned scoring function

Delete a store's trained weights and everything they were trained on.

Removes the trained model, the captured searches and the relevance signals collected for them, and stops applying the model to searches. The store stays opted into config.lsf: it starts capturing again immediately and retrains from scratch on the next run.

Args: store_identifier: The ID or name of the store.

Returns: StoreLsfCleared: Confirmation that the learned scoring function was cleared.