Revert "Add documentation for strange content type received from Internet Explorer"

Maybe I have to relearn how to read ...

This reverts commit d199e584.

lib/paperclip.rb

@@ -351,10 +351,6 @@ module Paperclip
     # NOTE: If you do not specify an [attachment]_content_type field on your
     # model, content_type validation will work _ONLY upon assignment_ and
     # re-validation after the instance has been reloaded will always succeed.
-    #
-    # WARNING: There's also some known issue with the content type sent by
-    # Internet Explorer might not be the same as other browsers. You can look at
-    # https://github.com/thoughtbot/paperclip/issues/68 for more information.
     def validates_attachment_content_type name, options = {}
       validation_options = options.dup
       allowed_types = [validation_options[:content_type]].flatten