don't set default Encodings in ruby 1.9

closes #CNVS-2165

This is recommended in some guides for upgrading a Rails 2.3 app to Ruby
1.9, but it was causing a lot of problems with file reading and writing,
especially in gems.

Our override for ActiveSupport::SafeBuffer to always be encoded as utf-8
fixes the issue that originally prompted us to add these default
encodings in the first place.

Change-Id: Ifb4649dd6aa86bfb15ff16daa706a5c6df33292a
Reviewed-on: https://gerrit.instructure.com/16079
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Ethan Vizitei <ethan@12spokes.com>
QA-Review: Brian Palmer <brianp@instructure.com>

config/initializers/ruby_version_compat.rb

@@ -132,7 +132,7 @@ else
   # (which in canvas is utf-8)
   class ActiveSupport::SafeBuffer
     def initialize(*a)
-      super.force_encoding(Encoding.default_internal)
+      super.force_encoding('utf-8')
     end
   end
 end

config/preinitializer.rb

@@ -14,7 +14,6 @@ begin
   # Set up load paths for all bundled gems
   ENV["BUNDLE_GEMFILE"] ||= File.expand_path("../../Gemfile", __FILE__)
   Bundler.setup
-  Encoding.default_internal = Encoding.default_external = 'UTF-8' if defined?(Encoding)
 rescue Bundler::GemNotFound
   raise RuntimeError, "Bundler couldn't find some gems." +
     "Did you run `bundle install`?"