Remove some more code added to support older versions

Also change back to run CI on ubuntu-latest which should work with all
Ruby versions supported now.

test/rails_app/app/controllers/streaming_controller.rb

@@ -8,16 +8,4 @@ class StreamingController < ApplicationController
   def index
     render body: 'Index'
   end
-
-  # Work around https://github.com/heartcombo/devise/issues/2332, which affects
-  # tests in Rails 4.x (and affects production in Rails >= 5)
-  def process(name)
-    super(name)
-  rescue ArgumentError => e
-    if e.message == 'uncaught throw :warden'
-      throw :warden
-    else
-      raise e
-    end
-  end
 end

test/test_helper.rb

@@ -23,22 +23,6 @@ end
 if ActiveSupport.respond_to?(:test_order)
   ActiveSupport.test_order = :random
 end
-class ActiveSupport::TestCase
-  if ActiveSupport.version < Gem::Version.new("5.0")
-    def assert_deprecated(match, deprecator)
-      super(match) do
-        # TODO: remove extra begin..end when dropping support for Ruby <= 2.4
-        begin
-          behavior = deprecator.behavior
-          deprecator.behavior = ActiveSupport::Deprecation.behavior
-          yield
-        ensure
-          deprecator.behavior = behavior
-        end
-      end
-    end
-  end
-end
 
 OmniAuth.config.logger = Logger.new('/dev/null')