Removing `squash_options` feature flag from code

* It's been enabled by default for a while so it should be safe to
remove at this point

app/views/projects/_merge_request_settings.html.haml

@@ -4,8 +4,7 @@
 
 = render 'projects/merge_request_merge_options_settings', project: @project, form: form
 
-- if Feature.enabled?(:squash_options, @project, default_enabled: true)
-  = render 'projects/merge_request_squash_options_settings', form: form
+= render 'projects/merge_request_squash_options_settings', form: form
 
 = render 'projects/merge_request_merge_checks_settings', project: @project, form: form
 

config/feature_flags/development/squash_options.yml

----
-name: squash_options
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/33930
-rollout_issue_url: 
-milestone: '13.2'
-type: development
-group: group::code review
-default_enabled: true

doc/user/project/merge_requests/squash_and_merge.md

@@ -110,7 +110,6 @@ squashing can itself be considered equivalent to rebasing.
 > - It's enabled on GitLab.com.
 > - It can be enabled per project.
 > - It's recommended for production use.
-> - For GitLab self-managed instances, GitLab administrators can opt to [disable it](#enable-or-disable-squash-commit-options). **(CORE ONLY)**
 
 With Squash Commits Options you can configure the behavior of Squash and Merge for your project.
 To set it up, navigate to your project's **Settings > General** and expand **Merge requests**.
@@ -133,31 +132,6 @@ NOTE:
 If your project is set to **Do not allow** Squash and Merge, the users still have the option to
 squash commits locally through the command line and force-push to their remote branch before merging.
 
-### Enable or disable Squash Commit Options **(CORE ONLY)**
-
-Squash Commit Options is under development but ready for production use. It is
-deployed behind a feature flag that is **enabled by default**.
-[GitLab administrators with access to the GitLab Rails console](../../../administration/feature_flags.md)
-can opt to disable it.
-
-To enable it:
-
-```ruby
-# Instance-wide
-Feature.enable(:squash_options)
-# or by project
-Feature.enable(:squash_options, Project.find(<project ID>))
-```
-
-To disable it:
-
-```ruby
-# Instance-wide
-Feature.disable(:squash_options)
-# or by project
-Feature.disable(:squash_options, Project.find(<project ID>))
-```
-
 <!-- ## Troubleshooting
 
 Include any troubleshooting steps that you can foresee. If you know beforehand what issues

ee/app/views/projects/_merge_request_settings.html.haml

@@ -4,8 +4,7 @@
 
 = render_ce 'projects/merge_request_merge_options_settings', project: @project, form: form
 
-- if Feature.enabled?(:squash_options, @project, default_enabled: true)
-  = render_ce 'projects/merge_request_squash_options_settings', form: form
+= render_ce 'projects/merge_request_squash_options_settings', form: form
 
 = render_ce 'projects/merge_request_merge_checks_settings', project: @project, form: form