Remove needless require "pp"

In Ruby 2.5 and later, `Kernel#pp` is automatically loaded.

https://bugs.ruby-lang.org/issues/14123

This changes remove the needless `require "pp"`.

actionpack/test/abstract_unit.rb

@@ -29,8 +29,6 @@
 require "active_support/dependencies"
 require "active_model"
 
-require "pp" # require 'pp' early to prevent hidden_methods from not picking up the pretty-print methods until too late
-
 module Rails
   class << self
     def env

actionview/test/abstract_unit.rb

@@ -24,8 +24,6 @@
 require "active_model"
 require "active_record"
 
-require "pp" # require 'pp' early to prevent hidden_methods from not picking up the pretty-print methods until too late
-
 ActiveSupport::Dependencies.hook!
 
 Thread.abort_on_exception = true

activesupport/test/dependencies_test.rb

@@ -1,7 +1,6 @@
 # frozen_string_literal: true
 
 require "abstract_unit"
-require "pp"
 require "active_support/dependencies"
 require "dependencies_test_helpers"
 

guides/source/initialization.md

@@ -405,7 +405,6 @@ def start &blk
 
   if options[:debug]
     $DEBUG = true
-    require 'pp'
     p options[:server]
     pp wrapped_app
     pp app

railties/lib/rails/application.rb

@@ -482,10 +482,6 @@ def helpers_paths #:nodoc:
       config.helpers_paths
     end
 
-    console do
-      require "pp"
-    end
-
     console do
       unless ::Kernel.private_method_defined?(:y)
         require "psych/y"