Remove branches_pagination_without_count FF

It should be enabled along with branch_list_keyset_pagination
feature flag anyway, so let's just replace the usage of
branches_pagination_without_count with
branch_list_keyset_pagination

Changelog: changed

app/views/projects/branches/index.html.haml

@@ -42,7 +42,7 @@
   %ul.content-list.all-branches
     - @branches.each do |branch|
       = render "projects/branches/branch", branch: branch, merged: @merged_branch_names.include?(branch.name), commit_status: @branch_pipeline_statuses[branch.name], show_commit_status: @branch_pipeline_statuses.any?
-  - if Feature.enabled?(:branches_pagination_without_count, @project, default_enabled: :yaml)
+  - if Feature.enabled?(:branch_list_keyset_pagination, @project, default_enabled: :yaml)
     = render('kaminari/gitlab/without_count', previous_path: @prev_path, next_path: @next_path)
   - else
     = paginate @branches, theme: 'gitlab'

config/feature_flags/development/branches_pagination_without_count.yml

----
-name: branches_pagination_without_count
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/50759
-rollout_issue_url:
-milestone: '13.9'
-type: development
-group: group::source code
-default_enabled: false