When using the 3scale toolbox to import a product via Product CRD the backends are automatically created and linked to the product.

The design of the `3scale product import` command is that it is meant to allow modifications to the existing product.yaml and reimport to apply the changes.

However, when changing the product.yaml definition to use a new backend but the same path the expected result is that it will create the new backend (if needed) and change the existing backend usage to use the new backend.

Instead, it will result in an error:

{
  "code": "E_3SCALE_API",
  "message": "Backend usage has not been created. Errors: {\"path\"=>[\"This path is already taken. Specify a different path.\"]}",
  "class": "ThreeScaleToolbox::ThreeScaleApiError"
}

It appear that this happens because the existing backend usage is not cleared first.