Refactor some code to remove warnings

[softr8]

price_in

Spree::Price#price_in will be removed from Solidus 3.0, and variant_decorator uses it throwing the following warning:

DEPRECATION WARNING: price_in is deprecated and will be removed from Solidus 3.0 (use price_for instead) (called from active_sale_in at /.../solidus_sale_prices/app/decorators/models/solidus_sale_prices/spree/variant_decorator.rb:26)

Price_on requires pricing options, not sure how to get the params required, maybe:

def active_sale_in(currency)
  price_for(Spree::Config.pricing_options_class.new(currency: currency))
end

discard

Spree::Price.with_deleted has been deprecated. Use Spree::Price.with_discarded instead. app/models/spree/sale_price.rb:6

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.