delete
Deletes a stored key so its keyId no longer resolves to a keyshare.
The SDK writes a ReconcileStoreDao with both currentKeyshare and stagedKeyshare set to null through the session's StorageClient. A StorageClient should treat that null-filled record as a removal; a simple implementation may keep it as a tombstone, since the SDK only ever reads non-null shares.
Return
Result.success once the storage write completes, or Result.failure if the StorageClient throws.
Parameters
keyId
the hex-encoded keyId to delete.