Remove scalability_ci_fetch_sha feature flag

We enabled the feature flag without trouble on gitlab.com so we no
longer need it.

app/presenters/ci/build_runner_presenter.rb

@@ -93,22 +93,10 @@ module Ci
     end
 
     def refspec_for_persistent_ref
-      #
-      # End-to-end test coverage for CI fetching seems to not be strong, so we
-      # are using a feature flag here to close the confidence gap. My (JV)
-      # confidence about the change is very high but if something is wrong
-      # with it after all, this would cause all CI jobs on gitlab.com to fail.
-      #
-      # The roll-out will be tracked in
+      # Use persistent_ref.sha because it sometimes causes 'git fetch' to do
+      # less work. See
       # https://gitlab.com/gitlab-com/gl-infra/scalability/-/issues/746.
-      #
-      if Feature.enabled?(:scalability_ci_fetch_sha, type: :ops)
-        # Use persistent_ref.sha because it causes 'git fetch' to do less work.
-        # See https://gitlab.com/gitlab-com/gl-infra/scalability/-/issues/746.
-        "+#{pipeline.persistent_ref.sha}:#{pipeline.persistent_ref.path}"
-      else
-        "+#{pipeline.persistent_ref.path}:#{pipeline.persistent_ref.path}"
-      end
+      "+#{pipeline.persistent_ref.sha}:#{pipeline.persistent_ref.path}"
     end
 
     def persistent_ref_exist?

config/feature_flags/ops/scalability_ci_fetch_sha.yml

----
-name: scalability_ci_fetch_sha
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/51208
-rollout_issue_url: https://gitlab.com/gitlab-com/gl-infra/scalability/-/issues/746
-milestone: '13.8'
-type: ops
-group: team::Scalability
-default_enabled: false

spec/presenters/ci/build_runner_presenter_spec.rb

@@ -196,16 +196,6 @@ RSpec.describe Ci::BuildRunnerPresenter do
       expect(subject[0]).to match(/^\+[0-9a-f]{40}:refs\/pipelines\/[0-9]+$/)
     end
 
-    context 'when the scalability_ci_fetch_sha feature flag is disabled' do
-      before do
-        stub_feature_flags(scalability_ci_fetch_sha: false)
-      end
-
-      it 'fetches the ref by name' do
-        expect(subject[0]).to eq("+refs/pipelines/#{pipeline.id}:refs/pipelines/#{pipeline.id}")
-      end
-    end
-
     context 'when ref is tag' do
       let(:build) { create(:ci_build, :tag) }