search: remove legacy 'search[sort]' params.

Remove support for the `search[sort]` param on certain index pages. This
hasn't been used for years, and it caused the `search[order]=` param to
be added to pagination links even when the order was blank.

app/models/artist.rb

@@ -502,7 +502,6 @@ class Artist < ApplicationRecord
         q = q.includes(:tag).where("tags.name IS NULL OR tags.post_count <= 0").references(:tags)
       end
 
-      params[:order] ||= params.delete(:sort)
       case params[:order]
       when "name"
         q = q.order("artists.name")