uploads: fix /uploads listing search not working.

Upload#search was declared as an instance method instead of a class
method.

app/models/upload.rb

@@ -178,8 +178,7 @@ class Upload < ApplicationRecord
     end
   end
 
-  concerning :SearchMethods do
-    def search(params)
+  def self.search(params)
     q = super
 
     q = q.search_attributes(params, :uploader, :post, :source, :rating, :parent_id, :server, :md5, :server, :file_ext, :file_size, :image_width, :image_height, :referer_url)
@@ -208,7 +207,6 @@ class Upload < ApplicationRecord
 
     q.apply_default_order(params)
   end
-  end
 
   def assign_rating_from_tags
     if rating = PostQueryBuilder.new(tag_string).find_metatag(:rating)