Remove Bullet from Gemfile

We've been ignoring what the Bullet gem reports for at least 6 years
(maybe more), but we were still updating the gem and maintaining the
code in `config/environments/` (which caused conflicts every time we run
`rails app:update` to upgrade to a new Rails version). Maintaining it
isn't a huge effort, but it's infinitely bigger than the benefits we get
from it, which are zero.

Adding `includes` everywhere we query for records would be a huge
maintenance effort and would make the code less readable, so I don't
think it's worth it. We might do it occasionally if we detect a
performance bottleneck.

We could also use a gem to automatically avoid the N+1 queries problem,
like Goldiloader [1], ArLazyPreload [2] or JitPreload [3]. Benchmarks
show that the performance improvements obtained by using these gems is
about less than 10% (it depends a lot on the page being loaded, though),
which IMHO doesn't justify adding yet another gem that patches
ActiveRecord and that could be incompatible with other gems doing so.

There are a couple of open pull requests (at the time of writing,
they've been open for about two years) in the Rails repository [4][5] to
automatically avoid N+1 queries as well. For now, we'll hope something
similar is integrated in Rails itself in the future.

[1] https://github.com/salsify/goldiloader
[2] https://github.com/DmitryTsepelev/ar_lazy_preload
[3] https://github.com/clio/jit_preloader/
[4] Pull request 45231 in https://github.com/rails/rails/
[5] Pull request 45413 in https://github.com/rails/rails/

config/environments/development.rb

@@ -79,15 +79,6 @@ Rails.application.configure do
   logger.formatter = config.log_formatter
   config.logger = ActiveSupport::TaggedLogging.new(logger)
 
-  config.after_initialize do
-    Bullet.enable = true
-    Bullet.bullet_logger = true
-    if ENV["BULLET"]
-      Bullet.rails_logger = true
-      Bullet.add_footer = true
-    end
-  end
-
   # Uncomment if you wish to allow Action Cable access from any origin.
   # config.action_cable.disable_request_forgery_protection = true
 end