Drop Bundler version installation

We no longer to need to specify a specific version of Bundler for a number of reasons:

1. Starting with Bundler v2.3, Bundler automatically installs the version needed in Gemfile.lock if it's not installed already: https://bundler.io/blog/2022/01/23/bundler-v2-3.html.

2. Most of the time GitLab Rails and other projects update Gemfile.lock with a recent Bundler version, so the build images will usually be out of date anyway.

3. We've already crossed the Bundler v2.3 mark: Ruby 3.1.4 ships with Bundler v2.3.27, and Ruby 3.2.4 ships with Bundler v2.4.19.

We dropped the Bundler software definition in Omnibus in omnibus-gitlab!6849 (merged), so it's time to do it here too.

This will eliminate the headaches we've had defining BUNDLER_VERSION in our CI pipeline images.

Relates to omnibus-gitlab#8368 (comment 1941438315)

After this MR, we'll no longer publish images with Bundler versions. All projects using images that include Bundler should be updated:

• https://gitlab.com/gitlab-org/quality/engineering-productivity/team/-/blob/main/.gitlab-ci.yml: gitlab-org/quality/engineering-productivity/team!223 (merged)
• https://gitlab.com/gitlab-org/quality/pipeline-common/-/blob/master/ci/base.gitlab-ci.yml#L15: gitlab-org/quality/pipeline-common!433 (merged)
• https://gitlab.com/gitlab-org/ruby/gems/gitlab_quality-test_tooling/-/blob/main/.gitlab-ci.yml: gitlab-org/ruby/gems/gitlab_quality-test_tooling!209 (merged)
• https://gitlab.com/gitlab-org/ruby/gems/dri/-/blob/master/.gitlab-ci.yml: https://gitlab.com/gitlab-org/ruby/gems/dri/-/merge_requests/11
• https://gitlab.com/gitlab-org/gitlab: gitlab!156116 (merged)
  • https://gitlab.com/gitlab-org/gitlab-qa: gitlab-qa!1325 (merged)
• https://gitlab.com/gitlab-org/quality/toolbox/-/blob/master/.gitlab-ci.yml#L11: gitlab-org/quality/toolbox!152 (merged)
• https://gitlab.com/gitlab-org/quality/triage-ops/-/blob/master/.gitlab-ci.yml#L41: gitlab-org/quality/triage-ops!2865 (merged)
• https://gitlab.com/gitlab-org/quality/gitlab-environment-toolkit-configs/pipeline-common/-/blob/main/.gitlab/ci/gitlab-qa.yml: https://gitlab.com/gitlab-org/quality/gitlab-environment-toolkit-configs/pipeline-common/-/merge_requests/1
• https://gitlab.com/gitlab-org/geo-team/geo-ci/-/blob/main/.gitlab/ci/.build-and-test.yml#L199: https://gitlab.com/gitlab-org/geo-team/geo-ci/-/merge_requests/24