Drop dmail filters.

Few people used dmail filters (~900 users in 5 years) and even fewer
used them correctly. Most people used them to try to block dmail spam,
but usually they either blocked too much (by adding common words that
are present in nearly all dmails, causing all mails to them to be
filtered) or too little (blocking specific email addresses or urls,
which usually are never seen again after the spammer is banned).
Nowadays the spam detection system does a better job of filtering spam.

test/unit/dmail_filter_test.rb

@@ -1,57 +0,0 @@
-require 'test_helper'
-
-class DmailFilterTest < ActiveSupport::TestCase
-  def setup
-    super
-
-    @receiver = FactoryBot.create(:user)
-    @sender = FactoryBot.create(:user)
-  end
-
-  def create_dmail(body, title)
-    CurrentUser.scoped(@sender, "127.0.0.1") do
-      Dmail.create_split(:to_id => @receiver.id, :body => body, :title => title)
-    end
-  end
-
-  context "a dmail filter for a word" do
-    setup do
-      @dmail_filter = @receiver.create_dmail_filter(:words => "banned")
-    end
-
-    should "filter on that word in the body" do
-      create_dmail("banned", "okay")
-      assert_equal(true, @receiver.dmails.last.is_read?)
-    end
-
-    should "filter on that word in the title" do
-      create_dmail("okay", "banned")
-      assert_equal(true, @receiver.dmails.last.is_read?)
-    end
-
-    should "be case insensitive" do
-      create_dmail("Banned.", "okay")
-      assert_equal(true, @receiver.dmails.last.is_read?)
-    end
-  end
-
-  context "a dmail filter for a user name" do
-    setup do
-      @dmail_filter = @receiver.create_dmail_filter(:words => @sender.name)
-    end
-
-    should "filter on the sender" do
-      create_dmail("okay", "okay")
-      assert_equal(true, @receiver.dmails.last.is_read?)
-    end
-  end
-
-  context "a dmail filter containing multiple words" do
-    should "filter dmails containing any of the words" do
-      @receiver.create_dmail_filter(words: "foo bar spam")
-      create_dmail("this is a test (not *SPAM*)", "hello world")
-
-      assert_equal(true, @receiver.dmails.last.is_read?)
-    end
-  end
-end

test/unit/dmail_test.rb

@@ -43,49 +43,6 @@ class DmailTest < ActiveSupport::TestCase
       end
     end
 
-    context "filter" do
-      setup do
-        @recipient = FactoryBot.create(:user)
-        @recipient.create_dmail_filter(:words => "banned")
-        @dmail = FactoryBot.build(:dmail, :title => "xxx", :owner => @recipient, :body => "banned word here", :to => @recipient, :from => @user)
-      end
-
-      should "detect banned words" do
-        assert(@recipient.dmail_filter.filtered?(@dmail))
-      end
-
-      should "autoread if it has a banned word" do
-        @dmail.save
-        assert_equal(true, @dmail.is_read?)
-      end
-
-      should "not update the recipient's has_mail if filtered" do
-        @dmail.save
-        @recipient.reload
-        assert_equal(false, @recipient.has_mail?)
-      end
-
-      should "be ignored when sender is a moderator" do
-        CurrentUser.scoped(FactoryBot.create(:moderator_user), "127.0.0.1") do
-          @dmail = FactoryBot.create(:dmail, :owner => @recipient, :body => "banned word here", :to => @recipient)
-        end
-
-        assert_equal(false, @recipient.dmail_filter.filtered?(@dmail))
-        assert_equal(false, @dmail.is_read?)
-        assert_equal(true, @recipient.has_mail?)
-      end
-
-      context "that is empty" do
-        setup do
-          @recipient.dmail_filter.update(words: "   ")
-        end
-
-        should "not filter everything" do
-          assert(!@recipient.dmail_filter.filtered?(@dmail))
-        end
-      end
-    end
-
     context "from a banned user" do
       setup do
         @user.update_attribute(:is_banned, true)