Reset I18n.local for each spec

This avoids a locale setting leaking from one spec to another. It also
means that we don't have to reset the locale in individual specs.

Also:

- `cookies` is reset automatically and we don't need to do that.
- Removed some unused code (German number format and helper methods).

spec/models/spree/variant_spec.rb

@@ -59,16 +59,6 @@ describe Spree::Variant do
   end
 
   context "price parsing" do
-    around(:each) do |spec|
-      default_locale = I18n.default_locale
-      I18n.with_locale(default_locale) do
-        I18n.backend.store_translations(:de,
-                                        { number: { currency: { format: { delimiter: '.',
-                                                                          separator: ',' } } } })
-        spec.run
-      end
-    end
-
     context "price=" do
       context "with decimal point" do
         it "captures the proper amount for a formatted price" do