Removing deprecation message and silencing method.

The deprecation rake task is no longer useful because the deprecated
methods have already been removed.

The method for silencing stderr has been removed since it was only
useful for `rake test:uncommitted` which was deprecated and removed.

railties/lib/rails/test_unit/testing.rake

@@ -3,19 +3,6 @@ require 'rake/testtask'
 require 'rails/test_unit/sub_test_task'
 require 'active_support/deprecation'
 
-# Recreated here from Active Support because :uncommitted needs it before Rails is available
-module Kernel
-  remove_method :silence_stderr # Removing old method to prevent method redefined warning
-  def silence_stderr
-    old_stderr = STDERR.dup
-    STDERR.reopen(RbConfig::CONFIG['host_os'] =~ /mswin|mingw/ ? 'NUL:' : '/dev/null')
-    STDERR.sync = true
-    yield
-  ensure
-    STDERR.reopen(old_stderr)
-  end
-end
-
 task default: :test
 
 desc 'Runs test:units, test:functionals, test:integration together'
@@ -52,11 +39,6 @@ namespace :test do
     task :db => %w[db:test:prepare test:all]
   end
 
-  # Display deprecation message
-  task :deprecated do
-    ActiveSupport::Deprecation.warn "`rake #{ARGV.first}` is deprecated with no replacement."
-  end
-
   Rails::TestTask.new(single: "test:prepare")
 
   ["models", "helpers", "controllers", "mailers", "integration"].each do |name|