Removes require 'spec_helper' from generated spec_helper

Fixes #855

Author: alindeman

lib/generators/rspec/install/templates/spec/spec_helper.rb.tt

@@ -2,7 +2,6 @@
 ENV["RAILS_ENV"] ||= 'test'
 require File.expand_path("../../config/environment", __FILE__)
 require 'rspec/rails'
-require 'rspec/autorun'
 
 # Requires supporting ruby files with custom matchers and macros, etc, in
 # spec/support/ and its subdirectories. Files matching `spec/**/*_spec.rb` are