Removes Debate.search & uses Debate.tagged_by when appropriate

Using `params` was wrong here because if given an inexistent tag,
@tag_filter was nil but the debates were still filtered by it (so the
listing and what the page title said were different)

app/controllers/debates_controller.rb

@@ -1,13 +1,15 @@
 class DebatesController < ApplicationController
-  before_action :parse_order, :parse_tag_filter, only: :index
+  before_action :parse_order, only: :index
+  before_action :parse_tag_filter, only: :index
   before_action :authenticate_user!, except: [:index, :show]
 
   load_and_authorize_resource
   respond_to :html, :js
 
   def index
-    @debates = Debate.search(params).page(params[:page]).for_render.send("sort_by_#{@order}")
-    @tags = ActsAsTaggableOn::Tag.all
+    @debates = Debate.all
+    @debates = @debates.tagged_with(@tag_filter) if @tag_filter
+    @debates = @debates.page(params[:page]).for_render.send("sort_by_#{@order}")
     @tag_cloud = Debate.tag_counts.order('count desc, name asc')
     set_debate_votes(@debates)
   end

app/models/debate.rb

@@ -35,14 +35,6 @@ class Debate < ActiveRecord::Base
   # Ahoy setup
   visitable # Ahoy will automatically assign visit_id on create
 
-  def self.search(params)
-    if params[:tag]
-      tagged_with(params[:tag])
-    else
-      all
-    end
-  end
-
   def likes
     cached_votes_up
   end

spec/models/debate_spec.rb

@@ -174,21 +174,6 @@ describe Debate do
     end
   end
 
-  describe "#search" do
-    let!(:economy) { create(:debate, tag_list: "Economy") }
-    let!(:health)  { create(:debate, tag_list: "Health")  }
-
-    it "returns debates tagged with params tag" do
-      params = {tag: "Economy"}
-      expect(Debate.search(params)).to match_array([economy])
-    end
-
-    it "returns all debates if no parameters" do
-      params = {}
-      expect(Debate.search(params)).to match_array([economy, health])
-    end
-  end
-
   describe '#default_order' do
     let!(:economy) { create(:debate) }
     let!(:health)  { create(:debate) }