The usage has been removed a while ago, let's remove the gem itself
from the Gemfile

The version we've been using - v5.1.0 - is more than four years out of
date. It doesn't include matchers for the use of
ActiveRecord::Encryption, which is important for us to have as we
migrate to ActiveRecord::Encryption from the attr_encrypted gem.

The version constraint on oj seems very strict, so let's relax it a
little bit, so that the version can be bumped independently in the
main lockfile.

- Fix breaking changes introduced by 0.28.0

This reverts merge request !172742

There are many RuboCop cops used internally, which have inline
documentation.

These cops can now have documentation generated for them automatically,
so GitLab developers and contributors can reference our documentation
and examples, to better understand the cops as well as the reasoning
behind our decisions.

The version constraint on json seems very strict, so let's relax it a
little bit, so that the version can be bumped independently in the
main lockfile.

Bumping the version of Truncato fixes a problem with mangled non-ASCII
characters in the `simple_search_highlight_and_truncate` method.

Changelog: fixed

Resynched with `bundle exec rake bundler:gemfile:sync`.

The version constraint on json seems very strict, so let's relax it a
little bit, so that the version can be bumped independently in the
main lockfile.

Changelog: fixed