Remove Spree::Product#currency getter and setter delegation to master
Remove Spree::Product#currency getter and setter delegation to master

Surprisingly, we do not have this method anymore on products and variants:

product.currency
NoMethodError: undefined method `currency' for #<Spree::Variant:0x007fdd2242a548>

product.currency = 'EUR'
NoMethodError: undefined method `currency=' for #<Spree::Variant:0x007fdd2242a548>

pervino/solidus,pervino/solidus,pervino/solidus,pervino/solidus