One should really use a separate table instead of using polymorphic
associations.

See https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/11168 for
more information.

... when the user is destroyed.

1. Normally, for a given awardable and award emoji name, a user is only allowed
   to create a single award emoji.

2. This validation needs to be removed for ghost users, since:

   - User A and User B have created award emoji - with the same name and against
     the same awardable
   - User A is deleted. Their award emoji is moved to the ghost user
   - User B is deleted. Their award emoji needs to be moved to the ghost user.
     However, this breaks the uniqueness validation, since the ghost user is
     only allowed to have one award emoji of a given name for a given awardable

This reverts commit cb10b725c8929b8b4460f89c9d96c773af39ba6b.

No reason to split it into a separate gem when the gem barely did anything. We can use gemojione directly, making updating gemojione that much easier.

Also fix the Rake task and update gemojione to 2.6.1. This adds the EmojiOne Spring update.

Changelog: https://github.com/jonathanwiesel/gemojione/blob/master/CHANGELOG.md