Remove merge_request_rebase_nowait_lock feature flag

Removes merge_request_rebase_nowait_lock feature flag added in 12.5

app/models/merge_request.rb

@@ -1899,11 +1899,7 @@ class MergeRequest < ApplicationRecord
   end
 
   def with_rebase_lock
-    if Feature.enabled?(:merge_request_rebase_nowait_lock, default_enabled: true)
-      with_retried_nowait_lock { yield }
-    else
-      with_lock(true) { yield }
-    end
+    with_retried_nowait_lock { yield }
   end
 
   # If the merge request is idle in transaction or has a SELECT FOR

changelogs/unreleased/320758-remove-merge_request_rebase_nowait_lock-feature-flag.yml

+---
+title: Remove merge_request_rebase_nowait_lock flag
+merge_request: 56406
+author:
+type: other

config/feature_flags/development/merge_request_rebase_nowait_lock.yml

----
-name: merge_request_rebase_nowait_lock
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/18481
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/320758
-milestone: '12.5'
-type: development
-group: group::code review
-default_enabled: true

spec/controllers/projects/merge_requests_controller_spec.rb

@@ -2048,21 +2048,6 @@ RSpec.describe Projects::MergeRequestsController do
       end
     end
 
-    context 'with SELECT FOR UPDATE lock' do
-      before do
-        stub_feature_flags(merge_request_rebase_nowait_lock: false)
-      end
-
-      it 'executes rebase' do
-        allow_any_instance_of(MergeRequest).to receive(:with_lock).with(true).and_call_original
-        expect(RebaseWorker).to receive(:perform_async)
-
-        post_rebase
-
-        expect(response).to have_gitlab_http_status(:ok)
-      end
-    end
-
     context 'with NOWAIT lock' do
       it 'returns a 409' do
         allow_any_instance_of(MergeRequest).to receive(:with_lock).with('FOR UPDATE NOWAIT').and_raise(ActiveRecord::LockWaitTimeout)