Revert "Add example label to activesupport/configurable"

This reverts commit f480b2ce.

Reason: API guidelines discourage this, see http://edgeguides.rubyonrails.org/api_documentation_guidelines.html#example-code

activesupport/lib/active_support/configurable.rb

@@ -33,8 +33,6 @@ def #{name}=(value); config.#{name} = value; end
 
     # Reads and writes attributes from a configuration <tt>OrderedHash</tt>.
     # 
-    # Example:
-    # 
     #   require 'active_support/configurable'      
     #  
     #   class User