Deletes classic test related to STI

Without classic, this test would be testing that Zeitwerk works. That
belongs to the test suite of Zeitwerk.

Active Record has the class available, whether it was already loaded or
pending autoloading, is not AR's concern.

activerecord/test/cases/inheritance_test.rb

@@ -376,17 +376,6 @@ def test_new_without_storing_full_sti_class
     end
   end
 
-  def test_new_with_autoload_paths
-    path = File.expand_path("../models/autoloadable", __dir__)
-    ActiveSupport::Dependencies.autoload_paths << path
-
-    firm = Company.new(type: "ExtraFirm")
-    assert_equal ExtraFirm, firm.class
-  ensure
-    ActiveSupport::Dependencies.autoload_paths.reject! { |p| p == path }
-    ActiveSupport::Dependencies.clear
-  end
-
   def test_inheritance_condition
     assert_equal 12, Company.count
     assert_equal 3, Firm.count