Update variantAutocomplete to use new search param

Instead of trying to generate some hardcoded Ransack search values, we
can use the APIs ability to use our Search::Variant class instead.

Author: adammathys

backend/app/assets/javascripts/spree/backend/variant_autocomplete.js

@@ -31,9 +31,7 @@
         },
         data: function(term, page) {
           var searchData = {
-            q: {
-              product_name_or_sku_cont: term
-            },
+            variant_search_term: term,
             token: Spree.api_key
           };
           return _.extend(searchData, searchOptions);