aliases/implications: change automatic retirement rules.

Change the rules for automatically retiring aliases and implications:

* Retire aliases to tags that are empty, or that are for a general or
  artist tag that hasn't received any new posts in the last two years.
* Retire implications from tags that are empty.
* Don't retire aliases or implications for character, copyright, or
  meta tags any more, unless the tags are empty.

test/unit/tag_relationship_retirement_service_test.rb

@@ -1,62 +0,0 @@
-require 'test_helper'
-
-class TagRelationshipRetirementServiceTest < ActiveSupport::TestCase
-  context ".forum_topic" do
-    subject { TagRelationshipRetirementService }
-
-    should "create a new topic if one doesn't already exist" do
-      assert_difference(-> { ForumTopic.count }) do
-        subject.forum_topic
-      end
-    end
-
-    should "create a new post if one doesn't already exist" do
-      assert_difference(-> { ForumPost.count }) do
-        subject.forum_topic
-      end
-    end
-  end
-
-  context ".each_candidate" do
-    subject { TagRelationshipRetirementService }
-
-    setup do
-      subject.stubs(:is_unused?).returns(true)
-
-      @new_alias = create(:tag_alias, antecedent_name: "aaa", consequent_name: "bbb")
-      @old_alias = create(:tag_alias, antecedent_name: "ccc", consequent_name: "ddd", created_at: 3.years.ago)
-    end
-
-    should "find old tag relationships" do
-      subject.each_candidate(TagAlias) do |rel|
-        assert_equal(@old_alias, rel)
-      end
-    end
-
-    should "not find new tag relationships" do
-      subject.each_candidate(TagAlias) do |rel|
-        assert_not_equal(@new_alias, rel)
-      end
-    end
-  end
-
-  context ".is_unused?" do
-    subject { TagRelationshipRetirementService }
-
-    setup do
-      @new_alias = create(:tag_alias, antecedent_name: "aaa", consequent_name: "bbb")
-      @new_post = create(:post, tag_string: "bbb")
-
-      @old_alias = create(:tag_alias, antecedent_name: "ccc", consequent_name: "ddd", created_at: 3.years.ago)
-      @old_post = create(:post, tag_string: "ddd", created_at: 3.years.ago)
-    end
-
-    should "return true if no recent post exists" do
-      assert(subject.is_unused?("ddd"))
-    end
-
-    should "return false if a recent post exists" do
-      refute(subject.is_unused?("bbb"))
-    end
-  end
-end