users: move sockpuppet detection from model to controller.

test/unit/user_test.rb

@@ -231,21 +231,6 @@ class UserTest < ActiveSupport::TestCase
       end
     end
 
-    context "that might be a sock puppet" do
-      setup do
-        @user = FactoryBot.create(:user, last_ip_addr: "127.0.0.2")
-        Danbooru.config.unstub(:enable_sock_puppet_validation?)
-      end
-
-      should "not validate" do
-        CurrentUser.scoped(nil, "127.0.0.2") do
-          @user = FactoryBot.build(:user)
-          @user.save
-          assert_equal(["Last ip addr was used recently for another account and cannot be reused for another day"], @user.errors.full_messages)
-        end
-      end
-    end
-
     context "when searched by name" do
       should "match wildcards" do
         user1 = FactoryBot.create(:user, :name => "foo")