Remove 'This guide is based on ' warnings.

It's obvious that the guide is based on this version of Rails, and may not be backwards compatible.

guides/source/action_mailer_basics.md

@@ -5,8 +5,6 @@ This guide should provide you with all you need to get started in sending and re
 
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-WARNING. This guide is based on Rails 3.2. Some of the code shown here will not work in earlier versions of Rails.
-
 Introduction
 ------------
 

guides/source/active_model_basics.md

@@ -5,8 +5,6 @@ This guide should provide you with all you need to get started using model class
 
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-WARNING. This guide is based on Rails 3.0. Some of the code shown here will not work in earlier versions of Rails.
-
 Introduction
 ------------
 

guides/source/command_line.md

@@ -13,8 +13,6 @@ Rails comes with every command line tool you'll need to
 
 NOTE: This tutorial assumes you have basic Rails knowledge from reading the [Getting Started with Rails Guide](getting_started.html).
 
-WARNING. This Guide is based on Rails 3.2. Some of the code shown here will not work in earlier versions of Rails.
-
 Command Line Basics
 -------------------
 

guides/source/getting_started.md

@@ -12,9 +12,6 @@ you should be familiar with:
 
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-WARNING. This Guide is based on Rails 4. Some of the code shown here will not
-work in earlier versions of Rails.
-
 Guide Assumptions
 -----------------